Well, first you get a spraypaint-can, then you get a horse...
Hm, no :P But I made this tuorial for another site and thought I could share it here too, if anyone's interested. :) It's made in Photoshop but should work for most programs and maybe get a hint on how you can work in oils or acrylic too.
Enjoy and please citisize, but not too much ;)
One of a thousand ways to draw a horse --the image is large.