Hello and Happy Halloween!
This is my first Instructable and one of the rare times I have ever tried to create a step-by-step document on my artistic process with SketchBook Pro on the iPad.

I really hope you find this informative and possibly helpful in exploring your creativity!

Thanks for checking it out and good luck to everyone!

Step 1: Halloween Painting on the IPad With Sketchbook Pro

The first step is to download the Autodesk SketchBook Pro app for your iPad if you don't have it!

I usually work on an HD canvas 1536x2048 as I tend to print my pieces an like the higher resolution. You get 6 layers on the iPad 3rd gen so layer management will be important to know when to merge. You can use the SD canvas @ 1024x768 if you prefere to have more layers and not feel the need to merge as often.

I decided to include these screen shots of the user interface of SketchBook Pro, iPad.
Of all the art apps for iPad, SketchBook Pro has my favorite UI.
The first image illustrates all the available on screen tools that are readily available. The second and third images show the Brush/Color editor and Layer window respectively.

Step 2: Initial Sketch

The first thing I do is sketch out a loose idea of what I might want to paint. In the case of the Halloween pic, I knew I wanted a Jack-o-Latern character so my focus was to start on the charater's head.

I tend to let pieces develop and work on single elements as at time to let each near completed element continue to drive the overall piece.
Or, it could be referred to as just doodling, experimenting and goofing off until something magical happens!

For the initial sketch, I like to use a relatively small pencil set to the lowest opacity up to about halfway full opacity. I will usually choose a color like a smokey blue-gray color as that tends to really help me when I start painting under the sketch.

Step 3: And We Start (blocking in Color)

Next, I will open a new layer and place it below my sketch. From here, I will start blocking in the base color with a medium to large brush at full opacity. It is okay to paint outside the lines as you can use the eraser to cut back and refine the shape.

My concept sketch is fairly loose and I tend to work on only blocking in one element of a piece at a time. For me, this helps me stay loose while developing the rest of the piece.

If you choose to sketch out more of the finished concept, you could block in other areas as well but I would suggest, at minimum, keeping the character's elements on a separate layer from your background and other elements in the composition.

This could come in handy if you need to resize something later and aloows you to stay flexible.

Step 4: Initial Shading

Next, I will lower the opacity on the sketch layer and then lock the layer transparency of my layer with the flat color. From here, I will start using the soft airbrush with darker shades of the base color to define the shapes in the jack-o-latern.

For shading, I typically pick 2 darker shades of my base color and some pure black (so I am working with 3 colors + black).
I will use the second darkest color first and use an airbrush larger than needed but really low opacity (1-3%).

Next, I will come in with the lighter of the two shades. But, make a few changes to the airbrush.
I will set the size to be smaller depending on how thick areas are within the object and set the opacity maximum level closer to 10%.

With the airbrush and the ability to change size and opacity settings there are a couple of things to remember.
1. If you set the size really small and then really large, the size transition will be fairly abrupt.
2. The rule above applies to Opacity as well.
3. These two settings occur within the overall stroke so you can airbrush perfom some rather cool stuff by limiting the length of each of your strokes.
For example, you can make really short strokes that will be small and light opacity as long as you lift the stylus/finger after a short stroke. Or pick a longer line and watch the size/opacity change from start to finish. This can help you from having to go back and change brush properties and hopefully speed up your process.

The key here is to experiment with the airbrush at various settings and stroke lengths until you feel comfortable with the reactions to your strokes.

Step 5: More Shading and Details!

In this stage, I have added a layer beneath my partially shaded layer to paint the negative spaces near black. Keeping this on a separate layer (for now) will allow me to make adjustments to the edges of the orange layer without accidenatlly painting into "unintended) areas as I have kept the transparency locked for the layer.

The nest stage is zooming way in (up to 400% or more) and adding some texture to the pumpkin's orange shaded layer. I really love the textures in SketchBook and you can achieve some cool effects by making adjustments to the size, opacity and spacing as well as using different textures on top of eachother.

At this point, I usually come back in with the soft, low opacity airbrush and add my pure black shading.
Make sure the layer transparency is locked., This will allow you to only paint where you previously painted without affecting outside area requiring a lot of erasing.

One of the tricks here is to not try and draw/paint on the outside edges. Instead, use a medium airbrush with low opacity and start your stroke outside the painted area. Slowly move the stylus/finger towards the edge and watch the airbrush gently spray only onto the painted area to give your contrast a nice and smooth transition.

Step 6: Detail Close Up of Pumpkin

A close up screen shot to show the detail and the brush and settings.

Step 7: Adding the Wacom Bamboo Stylus With a Wacom Bamboo

The next stage, I added the vine/neck folowing some of the same steps at the pumkin head. Being that the neck isn't a focal point, I was able to stay loose and not get too granular with the details.

My original thought was to draw a Wacom Pen but since I am doing this piece on the iPad with my Wacom Bamboo, I opted to to start drawing the Bamboo (being in my hand, it made for an easy reference)!
The line tool was used to make the straight edges and outlines for the stylus. After that, I used the same workflow used to color the pumkin head.

As with before, I draw elements on separate layers to that I can move/scale them as needed prior to merging the layers.

It is a good idea to try and only merge layers that have objects with space between them and on relatively the same plane of depth as it may come handy in later!

Tip: When drawing straight lines with the line tool, use a small pencil with the min/max size the same and set the min/max opacity the same.
If you need a parallel line like I needed for the barrel of the stylus, try this:
Duplicate the initial line layer and then move it using "Move" only. This will help from accidentally rotating/scaling the line.

Step 8: Layer Duplication...no Need to Reinvent the Wheel!

This next stage show the various elements I added to build up the character's arms. Lot's of zooming and attention to detail!
Still not 100% sure where I am heading with this image, but having fun!

Oh yeah, for the "fingers" on the left hand, just layer duplications of the Wacom Bamboo layer, scale and move!

Step 9: Neckline and Upper Torso

After merging all the layers, except the inital sketch, I started building out the remainder of the shoulder and upper torso on a new layer.

Step 10: Where Will He Put All His Treats (adding the Bag)

Trick or Treating requires a bag for your treats, so I started drawing this guy a paper bag (and added the red mid-section to his torso!
Then duplicated the layer and set to Multipy to darken up the bag.

Step 11: It Is All in the Hips! (Adding the Hip and Legs)

Not sure why, but this guy seemed like a red sphere would make a good hip section for him.

The red sphere was done using a small red brush at full opacity and the circle tool in SBP, then bucket fill. Drawn on a separate layer then moved and sized.

I accidently drew it too small and when I resized it, I noticed the outer edge needed some clean up so I carefully touched it up with a small red pencil set to mid-opacity.

Next step was to lock the transparency of that layer and then use a medium and large very soft airbrush for the shading. The sphere is compromised of the flat red base, two darker shades of red and then pure black.

Legs...well being that he is shaping up to be a cyborg-pumpkin-man, I went with one metal and one derived from a vine-like structure.

Step 12: Here's Looking at You! (Adding the Eye)

Now that I had most of the visible part of the character complete, I wanted to add something to up the scare factor a bit, but also keep it somewhat fun.

So, I decided this guy needed an eyeball hanging from the socket as that always seems to get an "ooohhh" out of people. I had this in the initial sketch and decided it definitely needed to be in the final image.

In the first image, added a layer on top of the character layer and sketched some loose muscle tissue on top then continued to paint and refine the tissue until I thought I hade enough.

Once complete, I added a layer below and painted in the eye. Since the character is facing the right side of the image, I placed the iris/pupil looking left to help steer the viewer back into the image.

Once happy with it, I merged the eye layer with the character layer.

Step 13: Sidewalk and Lamposts!

Now that the character is nearly complete, I wanted to started working on the background. Since I didn't really sketch a great background, I needed some time to think. During this time, I decided that since I love SketchBooK Pro; I should add the logo to his bag. I hand drew the logo (iPad App logo) using the pencil tool. And of course, on a separate layer until I was happy with it and merged it down.

During this time I decided that this guy should be out tricking and treating and felt a nice sidewalk setting may make it seem like he is in a neighborhood somewhere.

Sketched some rough lines on a layer and then proceeded to paint the lamp posts using the straight line and ellipse/circle tool.

Once the first was complete, duplicated the layer and scaled/moved the second one up and to the right!

Next step, the porch and yard.

I wasn't too concerned about conveying his stepping into the street for two reasons:
1. I think most traffic would stop for this guy.
2. He looked both ways before stepping into the street.

Step 14: The Porch

For the porch, I used bit of a different tactic to create the basic shape.

I flood filled a layer (behind averything else) with a good blue color to contrast the other elements. Then, I went to the layer transform to rotate move the layer off the page some. Once I was happy with the angle of the bottom line, I tapped "done".

This cuts off the layer and creates the shape I needed after a few moves and trabsforms to the layer. I have found using the tool to move layers off the page and saving to cut shapes to be a pretty cool method for creating block-style shapes with very precise edges. Using the line tool with the eraser works as well but, I find I have a lot more control as I can rotate, move and scale the layer mutliple times before commiting "done". With the line and eraser tool, it seems like I was spending more time making the stroke and then if not perfect, undo and repeat until I had it right.

I takes some practice and sometimes a few attempts but, I really like using this technique.

I set the sidewalk and porch to have some perspective conflict as I am just weird in that I like some obscurity/surrealism in my work.

From there, it was on to locking the layer opacity and painting in the details.

At this stage I still have the character on a separate layer from the sidewalk and background.

Step 15: Light and Porch Detail

Just a quick snapshot to show the details!

Step 16: The Yard and Lights!

As you can see from the image, I am nearing completion of the image.

The next step was to add a layer to fill in the grassy areas on either side of the porch. I did this by placing a layer on the bottom of the stack and then filling in with a nice dark blue-green color. Then painted in the grass with the "grass" brush.

Being that the standard green grass brush was too bright and I felt that overall the background was too bright for a night scene, I then added a layer behind the character and flood filled with a dark blue.

From there, I set the layer to Multiply and went back with the soft eraser to remove some of the blue layer in key areas that I wanted more light to show (the light from the lamps and parts of the sidewalk surface).

Next, I reduced the opacity of the layer to 50% to reduce the overall effect but still cast a nice bluish hue to most of the background as well as the top of the porch.

Step 17: Finishing Up!

At this stage, I am just about complete. I added a layer back on the very top and used the soft airbrush with a pale yellow color to add some soft light to the lamps and and highlights on the shoulder and neck. This was done to convey a sense that the door was open and ambient light was coming from the house. I went back in and used the pencil to touch up some small areas I missed as well as darkened up a few lines. Then added my signature, using the text tool, in the bottom right corner.

Keep in mind that a lot of this work was completed via zooming in a much as 1700% and lots of erasing and trial and error!

Step 18: Completed Image

Final image was exported as a PSD file to iTunes as I wanted to make some slight contrast adjustments to the character and the background.

It would have been easy enough to load individual layers, or the whole image, into a photo editing app to adjust the contrast and saturation.

But, worry not, I made the slight changes using SketchBook Pro V6 desktop!

So, all SketchBook Pro!

Thanks for taking the time to read through my first Instructable and Happy Halloween!