I usually begin painting from the inside out here, i.e. flesh to cloth to armor; theres less chance of accidentally making a mistake and getting paint on a previously-painted part that way. Picking a color scheme for the miniature also gives you an idea of what areas to paint first, too. Dark paints cover up light ones easily, not vice versa, so if you accidentally get flesh color all over another area that's supposed to be black, no problem! But paint black on an area that's supposed to be flesh and you'll have to use some white paint to re-primer over the black mistakes, before painting the flesh color section, since the flesh paint won't cover the black up.
Be careful with metallic paints, too, since they're notorious for getting flakes on surrounding areas of color when you're drybrushing or washing with them. For that reason, if the miniature has an metal to paint, I paint the metallic colors first, then prime over any mistakes, and paint all the other colors.
Your painting should start with a good foundation: the basecoat. This is the initial layer of paint that youll be doing all of your other work (drybrushing or blending) on top of. You want the basecoat layer to cover well, but not be so thick that it obscures fine details. A good rule of thumb is mixing the paint with water about 3 to 1; it should look sort of like heavy cream. If the first coat seems too thin (primer shows through), then paint on a second one. I cant emphasize enough, though, that the paint shouldnt be too thick! A few thin layers is better than one, goopy layer...
Washing and Drybrushing
This is a relatively easy painting technique, but it can yield some nice looking highlights. Begin by looking at your basecoat color and selecting a shade of paint one step darker than it; for example, a blue would need a royal blue or dark blue for a wash. Thin some of this dark paint in your palette with enough water to give it the consistency of low-fat milk (seems corny, but thats how it looks). Dip a medium sized brush (0 or 1) into the mix and paint the wash all over the basecoated area.
The thinned paint will flow easily and enable it to 'wash' or darken the underlying color with a translucent layer; when this dries, itll form natural shadows in the recesses of the basecoat, but still let some of the lighter color underneath show through on the highlights.
To further accentuate these highlights, you'll need to 'drybrush' them. Make a lighter shade of the basecoat color , by mixing it with a light color (i.e. sky blue with blue), or some white paint, for your drybrush color. Dont thin this paint down. Youll need an old, worn out paint brush for what comes next: begin by dipping the brush in the drybrush shade. Now take a paper towel and wipe off the excess paint from this brush; keep wiping until the paint seems to be gone, and rubbing it on the towel leaves barely any amount of color.
Next rub the brush over just the highlights of the area youve washed. Try not to push too hard here, or you can get thick splotches of paint; instead let the paint flakes in the bristles do the work. When youre done a nice highlight should appear on the area youre drybrushing. A little paint may have flaked into the shadows; a gentle breath or a separate brush will dislodge it while it's still drying.
If the highlight isnt strong enough for you, repeat the steps. Just thin each successive wash down with more water, so it doesnt completely obscure the highlight color you lay down with each drybrush. Ill sometimes do 2 to 4 layers of wash/drybrush in this way to get a desired look; this is especially good for textured areas, such as fur or hair. If the color you're doing is light enough, you can even do a drybrush of pure white as a final layer.
If you want to get more advanced, make each wash a little darker by adding even darker paint each time, and each drybrush color lighter; rather than doing the entire area each time, try to wash less and less of the surface, by running the brush closer to the shadows with each wash. Simultaneously, drybrush less and less of the highlight, until you are only covering the smallest top bit of the area. This makes for some nice effects when done right, but takes patience.
Ink Washes and Drybrushing
Another quick, but effective, method is using ink to wash the basecoat instead of paint. The wash/drybrush method is the same as outlined above. Use a few drops of water at most to thin inks, however, as over-thinning them results in them drying too quickly and unevenly, creating splotchy-looking washes or leaving ugly rings of color around the deep shadows, without depositing any actual color in the shadows, where it should be.
Since you'll be using the inks almost straight from the bottle, select colors which would make a good variety of wash shades for your paints. Citadel has a good range of colors (they now even call their inks washes), so chances are you can find a suitable shade for any color. An art supply store is also a good source of inks, but avoid ones which are marked permanent or water-proof'. Just remember that inks can look much darker than paints, because of their very vivid pigments. Some, such as purple and brown, definitely need thinning to use as a wash.
Where inks really shine is in making washes for metallic paints. They provide good shadows for the metal, but since they're transparent, they dont dull the metallic look, like paint washes do. Some good inks for metals are: brown or yellow-brown for gold, blue for silver, and red-brown for brass.