I picked up these carving ideas from a neighbor of mine when I was a kid. His Jack O'Lanterns were real lanterns - brightly lit and intricately carved. I learned that the trick is to scrape out the insides until the whole pumpkin is translucent, and gives off a beautiful orange glow.
Step 1: Getting the Tools Together
This is pumpkin carving - it's not like you need a lot of tools. I use a scoop, some wood-working gouges, a couple of knives and a bucket to hold the pumpkin insides. Also, I find wearing latex or nitrile gloves helps a lot when you are scraping the insides. Pumpkin is a bit acidic, and it can irritate the skin after a while. I also use a trouble light to check the thickness of the shell.
Step 2: Cut Open the Pumpkin
Insert the knife at a 45 degree angle into the top (stem end) of the pumpkin, and work it around the top until the cut is all the way around. Pull out the cut section. I usually discard this part.
Step 3: Scrape It Out
Pull out the stringy bits and seeds. Keep the seeds for toasting! The start scraping out the insides.
I made a scoop by removing the handle from a cheap ladle I bought at the dollar store. It fits nicely inside the pumpkin so I can scrape in all directions. I usually scrape around the axis, then from top to bottom. Keep one hand on the outside and scrape against it. The idea is to get the shell as thing as possible without scraping right through. The finished shell is about 1 cm thick, maybe even a bit thinner. Check the thickness with a trouble light or other lamp that you can fit inside the shell. The shell should light up evenly. If any areas show up dark, scrape them out a bit more.
Step 4: Carving
Now it's time to start carving. The big hole will be the bottom of the Jack O'Lantern, so flip it over so you can get the right orientation.
If you want, you can map out the design first using a marker. I usually just dig in, and see where the blade takes me.
I use woodworking gouges to make the designs on the surface. The idea is to peel the hard orange layer off, leaving the white flesh exposed. This lets the light out in a nice, diffuse glow.
I use the "V" gouge a lot. It allows me to make very fine lines. Run the gouge just about parallel to the surface, peeling up the orange outside layer. Use a flat gouge to remove larger areas, or experiment with different shapes of gouge.
Step 5: Special Effects
A cool effect is to make "hair" using the gouge. Run the gouge under the skin, but don't lift the skin right off. Back the gouge out so that the skin is still attached. it will curl up away from the shell. If you do this over a large area, it starts to look like hair or feathers.
Step 6: Add Some Vents
I'm a purist in that I use candles in the Jack O'Lanterns when possible. Since the shell is pretty much intact, it will need some vent holes to let air in and smoke out, if you are going to burn a candle inside. I poke a few holes in the top (the side away from the big hole) using the gouge. If necessary, I will cut notches along the bottom (big hole) to let more air in.
Step 7: Light It Up!
Light a candle and place the Jack O'Lantern over it. Bask in the warm, Halloweeny glow! Here's a few examples to give some more ideas.