Here is a brief tutorial on the methods I use to paint. The model is a 15mm Ground Zero Games figure, but I use the same system on 20mm and 28mm figures, and something similar for 6mm/micro armor.
The start: Army Painter paint brushes, my colors (Vallejo Yellow Green, Vallejo Dark Blue Grey, Army Painter Uniform Grey, generic white, generic black, and Army Painter Soft Tone Ink; model primed grey with Krylon automotive primer). The model is based on a penny, with crushed walnut shell glued on as texture.
Step 1: Paint the whole model in the base color, Vallejo Dark Blue Grey.
Step 2: Paint the weapon yellow green and the backpack uniform grey.
Step 3: Paint the goggles and sensor/sight looking things black.
Step 4: Apply the wash. I apply directly from the dropper, using a generous amount. I drip the wash onto the model and then paint it on with a brush.
Step 5: Let the wash dry. With some colors—drab military colors—you could actually stop at this point. But I want the model a bit brighter.
Step 6: Highlight the armor and the gun. I do this by mixing the base colors with a bit of white and applying them, drybrush style, to the model. I do two highlights, with more white in the second.
Step 7: Paint the base with Army Painter Desert Yellow. Highlight the base with Army Painter desert yellow + white. Done!