The Foundry three-color system is about the easiest painting method you can undertake. It also leaves a lot of room for different techniques (stippling, blending, drybrushing, impressionistic strokes.) The core to the system is having, for each color in your palette, three separate shades of color -- a base color, a midtone and the highlight color. So, for example, red might have brown as its base color, then the red, then either a pink or an orange for a highlight.
You start by applying the basecoat with your darkest shade. Next, you apply your midtone. Paint this middle shade on either raised areas of the sculpt, or on areas that are exposed to light. By leaving the areas out of the light with only the basecoat on, you've created a simple "shade" effect. Next, paint the highlight conservatively on the apex's of wrinkles, creases and folds, and also on "rim" areas like around the edge of a shirt or pant cuff. Again, keep the highlight on areas that would be exposed to light.
You can vary the degree of "jump" between shades in your 3-color palette so as to vary the contrast of your mniature. You an also add shades to your palette, so instead of a three-color system, you could be using 4-, 5- or even more shades per color.
If you want a good reference guide (with LOTS of step-by-step guides), I'd recommend Kevin Dallimore's painting guide by Foundry. I actually think it's worth the price.
You can find it here: http://www.wargamesfoundry.com/books/paintbook.asp
This system is a beginner's technique. It's simple anad easy and will produce figures ready for the tabletop. If you want to paint figures for display, I would expand the three color system to one of the multiples I mentioned- up to 10 shades if you have the patience. But, at that many shades, you might want to start learning other techniques such as blending.
Just a note: One of the reasons I like the three-color system is that I don't have to do washes. Washes are a great beginner technique, however, and can be used to great effect. But, I've never been able to control a wash as well as paint on the brush. Also, it takes time for the wash to dry before you can apply another layer of paint or varnish, and I like to get my figures painted quickly, so they can get onto the battlefield.
