Take a look at Swanny's web site for weathering techniques - www.swannysmodels.com/
I'm just getting back into modeling after a lot of years off. I tried Swanny's acrylic wash with what I thought were pretty good results. I think the key is getting a good sealer coat of Future on the model as a base for the wash. The method I use is: Paint the model with Tamiya acrylics, Future (at least two coats), apply decals, Future again, wash, Future one last time, and apply a dull coat. Be sure to allow the Future to dry for 24 hours or more.