Right. Firstly, let me state, if your going to paint fabric, find some referances. i NEVER work without a referance to look back on. the human mind is good, but not that good. ALSO remember where your lightsource is coming in. the fabric i chose to work with here should resemble satin.
right, firstly...a shape, with a midtone
then, you want to add your shadows. pay attention to areas that crease, like under busts, around armpits, or where ever there is a bend or tension in the fabric. this is where your referance comes in handy
now, add in the highlights. remembering where you lightsource is, add them at the highest points in all the folds, blending down into the rest of the fold
finally, give the highest points a once over with the dodge tool, just to give them a little more shine and express they are higher than the rest.
thats how i do my fabrics. in the next installment, i will show you how to add designs/embroidery and some other fabrics.