I'm no expert, but I will admit that I have a few shortcuts for lighting effects when it comes to Photoshop.

Here's a way that I use for the occasional cel shaded piece. Create a layer and lay down some colors for the character in question--usually what I do is set the flat colors and any fur/clothing patterns at this time in the base colors. Pick two colors to represent the highlighted area and the shadow cast on the unlit portion of the character. If references are available you can get an idea for the degree of contrast such as http://www.pkwy.k12.mo.us/west/teac.....ndIsOnFire.jpg or http://static.howstuffworks.com/gif.....reathing-7.jpg, though these are possibly overstated cases. With an idea for how much contrast there can be, creating several layers (usually for me with the shadowed layer at the bottom of the stack and the highlight at the top, with the base color in the middle), and using a mouse, or a tablet, or Photoshop's pen tool, draw out the layer to the general shape of the character's body that you wish. This tends to be a little time consuming though and it's tough to do for creatures with notable patterns such as tigers and leopards.

Another way is similar, but requires less messing around with colors. This time, set the base colors and patterns on a layer, and then create another layer or two--on top, use colors such as light gray or white to color in the highlighted areas and darker grays and black to fill in the shadowed parts. This may be on one or two layers as you please. This also helps in that it lets you use black and white fills to shade or highlight the image. When you're satisfied with the dispersal of light and dark, change the blending option on your black and white layer--this will usually be found in a drop down menu next to the opacity scroll bar in the 'layers' palette. I've found that options such as 'overlay' tend to produce the best results, though options like 'soft light' can be useful at times.

The last way is the most direct and comes with the most permanent and difficult-to-reverse changes to a color layer, so I recommend saving backups or using the history function if you try for this method. Once again, create a layer and put down the basic colors and pattern of the character or item. However, instead of creating new layers, you will end up modifying just the one layer. Using the Dodge and Burn tools in the tools palette, you can quickly brush over the desired highlighted and shadowed areas, respectively. Some tinkering with the highlights/midtones/shadows settings and the percentage of exposure (all in the tools option taskbar or window) may be necessary to achieve the desired effects and location. Needless to say this method really calls for a lot of trial-and-error--thus, the use of backups and lots of history-resets. However, it can create very pronounced areas of light and darkness, especially if using the softer brushes in Photoshop; I like that, but your mileage may vary.

Hopefully this bit of advice was helpful--again, I'm no expert and there's probably tutorials that can show demonstrate this better than I can explain it, but a quick, cursory search didn't offer anything promising immediately...most of the fire or lighting effects tutorials tended to deal with creating fire or messing with the Lighting Effects filter. Perhaps someone might have better luck than I did finding something more demonstrative, and less wordy.

In any case, good luck with digitally coloring your art. =3