first, i hate washes. they are hard to do, but heres my 2 cents. I first spray a gloss coat over things, let it dry, then with watered down "citadel" black ink i do a wash in the nooks and crannies with a very fine brush 10/0 or 20/0 i find is best. have a few ear cleaners on hand too to get rid on excess wash, only do small sections at a time too.
i picked up the technic from other guys' in our hobby club, and after trying several ways found this the easiest and most effective.
citidel paints can be found in any Games Workshop or good hobby shop (as a tip, get the one with the flip top lids, the screw tops dry out to fast)
experiments are the key to suceeding in doing a wash, as my collection of half finished 1/72 Airfix kits proves