Do check out http://beroleagle.deviantart.com/ar.....ushes-96742060 .

Thank you

Yeah, DA is full of Brushes. It has stuff for Photoshop and GIMP, I'm sure there'll be some SAI stuff.

http://www.pixelovely.com/gesture/f.....uredrawing.php

brushes are nice, but for overall improvement of the form of your characters, check this out.
do some gesture sketches. there are plenty of tutorials on how to make a gesture sketch look solid.
you're basically going to teach yourself anatomy the hard way - from observation of the body,
but honestly, it's the best and most efficient way to do it.

here's some tips on gesture drawing:
http://www.art.net/~rebecca/LifeDrawing1.html

i used to have some really good tutorials but i can't find them right now.