#1 Primer coat.
Spray or brush on. A primer coat gives you a foundation to paint your base coat. You can paint on bare plastic or metal, and I've done it. A primer coat makes things much easier and nicer though.

#2. Base coast.
The basic colors. I often think of coloring books, all you have to do is color "inside the lines".
#3. Wash.
Using a darker color, (dark blue, black, dark grey, whatever fits the base coat colors.) that's been watered down. This gets into all the cracks and crevices and makes details stand out from the base coat. If you use the Foundation line from Games Workshop, it also tends to make the foundation paints darker and richer.
#4. Highlights and details.
Drybrushing is when you load a brush with paint, and then wipe off all but a little bit of the color. Overbrushing is when you wipe off some of the paint until it's tacky. Both are useful techniques. Use a dusting motion with a big brush for drybrushing. If you see paint on the miniature after the first stroke, it's too much. Drybrushing should take a few strokes to see a difference.
With overbrushing, you should drag the brush over the raised surfaces of the model. Leaving paint on the highest edges.
These Genestealers were done with Games Workshop's Foundation, Wash and Color lines of paints.