As for photoshop help, I have this to offer (and I will have examples of past art listed at the end):
1. When you draw something, Ink it cleanly with a black pen of sorts. I use Alvin drafting pens or Staedler (spelling??) pens of various tip sizes.
Erase EVERYTHING you don't want to keep. When you do the pencils, use a hard lead and draw lightly so you can get rid of it. It makes things easier.
2. Scan the drawing in. I leave mine at a reasonably large size.
3. Desaturate and up the contrast. Though the pen may be black, your scanner may see delicate colors you don't want.
4. Now that you've got crisp lines, copy the entire thing (after saving as a file for the sake of having the outline saved in case of a goof-up) and make a new document in Photoshop. Make sure it's set to RGB. CMYK is a pain in the neck and grayscale is no help. Paste it. This way, it wont be the background layer.
5. Select the layer of your line drawing. In the layer mode, make sure it's set to MULTIPLY and not normal. This way, the black lines reign supreme. Now lock the layer. Make sure it's the top layer as well.
6. Make a new layer. NAME IT COLORS (or a specific area like "Hair" if you're doing anything with a lot of stuff).
7. go back to the lines layer and use the magic wand (set at 60 or above toleration) and select the area you want to color.
8. Now go to the COLOR layer and in the selection, color it with the paintbrush or whatever you use.
9. Repeat steps 7 and 8 until you've got the flats laid out. This is pretty much where I stopped on the weird al calender.
10. to create HIGHLIGHTS and SHADOWS, this is what a friend taught me and I'm pleased with it. I used this method to color a few collabs with her.
Take the area you want to do shading/highlighting on. Say... the arm of someone for example.
With any selector tool, select an area of the arm. Any area will do.
11. Go to IMAGE > ADJUSTMENTS > BRIGHTNESS/CONTRAST.
12. If you want to make a shadow, lower the brightness a little bit. Compare outside the selection to see how much of a contrast you want. hit okay.
13. Use the eyedropper tool. Select the dark area and NOW, go hit edit undo. It will remove the change you made to the arm.
SPECIAL NOTE: In theory, you could stop here-- it's a slow process though where you select everything you want to shadow, and just reduce the brightness. I find it's easier to hit undo and use the color I've selected to fill in areas. Once I get a shadow color for skin, I use it on all the skin areas. It also will look better if you take the time to do each part.
14. I use the polygon lasso tool for this next step. On the color layer, I choose the area I want to have a shadow on. Carefully with the lasso, I select the area. The smoothness of the selection is up to me. I've done some pieces where I need a smooth flowing curve, and others where jagged selections are the best. It all depends and with a few tries, you can get the hang of the tool to suit your need. To get a smoother curve, you will need to work really close on it (zoomed) and make more click points and move gradually. It takes some patience.
15. Once you have the area of the arm (or whatever) selected, you can paint in this area with the paintbrush.
16. Now you have a shadow. Making it look realistic takes pratice, trial and error. Observe how shadows fall. I clip photos out of magazines so I can reference how light falls on limbs and stuff, depending where the lightsource is.
17. Once you've done this with everything (ALWAYS SAVE ALONG THE WAY, AND SAVE FILES AS NEW FILES. YOU WILL THANK YOURSELF FOR BACKING UP PREVIOUS VERSIONS OF A PIECE SO THAT YOU CAN TRY NEW THINGS IN THE FUTURE WITHOUT HAVING TO REDO IT ALL FROM SCRATCH). you can blend if you choose.
I don't always blend, but if you want a nice soft shadow or change in color, this will help.
18. Select the color layer and choose the BLUR tool. On the Photoshop tool bar it looks like either a waterdrop, a pointing hand, or a triangle. The took has 3 functions: Blur, Sharpen, and smudge. You want the waterdrop. Smooth.
Select the smooth tool and use it to smooth out the edges where 2 different colors meet, or the whole thing. Depends on what you need.
Always test things out. Sometimes you need less pressure and change and other times you need more.
19. Now you've got your shadow. the whole thing works for highlights too. On step 12, you would select the brightness and raise it a little bit. Reference some examples for where light falls, and tweak the picture by selecting an area, coloring it with the new highlight, and then blending it.
I don't know a ton about doing this, and I don't have some amazing pieces, but it works. I've seen some juicy art that's so well colored it seems to feel real almost. A lot of comic art has this these days.
anyhoo... I hope I helped without going TOO overboard. Rather than just start halfway, I figured I'd outline the whole process of coloring and shadows/highlights.
Avoid the Dodge/burn tool at all costs. it's messy and discolors your art.
Some examples of my coloring can be seen here:
http://www.deviantart.com/deviation/7754153/ : A collab with the girl I mentioned above, who showed me this highlight/shadow method. She draws a lot of amazing stuff and I color things for her sometimes. This is the fairy godmother from Shrek 2 (not weird al related... I know... but it illustrates a gentler method of the highlight/shadow method). She had already shaded with the pencil and because I used MULTIPLY, the layer kept it's gentle pencil marks and allowed me to color without coloring OVER it.
http://www.deviantart.com/deviation/6262016/ :Here's the way my coloring regularly looks now. It's more crisp than the last piece, but the highlights and shadows are still blended a little. This was a get-well card I did for a voice actor. (again... not really Weird Al related at all, but used for example). You can click the picture to get the larger, better version so you can see how I colored/shaded/highlighted.
http://www.deviantart.com/deviation/3975290/ : This is dodge and burn. I colored this art by comic artist John Delaney and added it to the gallery with gracious permission from John. The colors and the highlights are much more harsh. It goes almost to white in some areas. This is a lazier method of highlight/shading. it worked for the look I was going for. I guess this IS distantly Weird Al related, because when I met him (3rd time, hehe) after the concert in Portland, Maine last July, he had a Brak show t shirt on. If memory serves me, he was on Space Ghost (or was that an old episode where some cartoonist DREW Al in to a story--- quite strange).
The dodge and burn works like a paintbrush. You click and hold and drag over stuff but it's very uncontrolable and messy. Dodge is the highlights that start to go white and have often done damage to delicate areas. Burn does that. It burns it darker.
You will notice that when you use Multiply for the lines, everything colored goes under the lines. That keeps things clean and filled without that annoying "oops, I colored OVER the lines" mess.
Anything white on the line drawing will become invisible. The color on the layer below it will still come through. You can also toy around with layer transparency for effects. That would be the opacity on the layers menu.