Welcome to a rather simple tutorial! I'm also in the process learning how to digitally paint myself (and by no means do I think I'm really spectacular at this) but this may be of some use to someone. Also, my drawing utensils consist of a Wacom Bamboo tablet and Photoshop CC. Let's get started ~~~! Ｏ(≧▽≦)Ｏ
Step 1: Sketch
Start with a digital rough sketch. In this tutorial, we are going to use Shiro from Deadman Wonderland as our muse.
Step 2: Begin Linework
Lower the opacity on your sketch layer and make a new layer on top. Begin to refine the linework with more precise brush strokes. In this step you can also choose to play around with the color of your lines, as well as horizontally flip your canvas to make any adjustments to the symmetry of the face.
Step 3: Refine Linework
In this step, we have turned "off" the sketch layer in order to preview what our lines look like. Snazzy, huh?
Step 4: Choose Color Palette
When painting, I find it easiest to either manually choose colors using the color picker or go online and find a pre-made palette to incorporate into my drawing. Then, I sample each color to the side of the image so that it's easier and faster to eyedrop from your color palette whilst in the middle of painting. I also chose to keep my sketch layer visible underneath my lineart.
Step 5: Begin Painting
To prepare for laying color down, I grouped the sketch and linework layers together (*not* merged) and set the layer blending option on this group to "Multiply". Then, I create another empty layer beneath the group and designated it specifically for my colors. You can also begin to add more colors to your painting palette as you progress.
Step 6: Continue Painting...
Although this piece is obviously unfinished, it has a pretty solid start: basic colors, a scheme or palette, and blocks of shading. You can also choose to experiment with the color of the lineart itself by selecting the lineart layer and going into Image > Adjustments > Hue/Saturation (in Photoshop). With these simple techniques, you can really start to see some cool effects!