Besides all the things mentioned in the VAN's article noted by the previous poster, one item is not stated. Yes, thinning the trailing edge of the light wing will cause that wing to drop, but you can also "Fatten" the trailing edge of the heavy wing by holding a piece of 2 X 4 along the trailing edge and hitting it (not too hard, now) with a hammer. My method was to start at one end of the 2 X 4 and go along the length of the aileron.
The reason I share this is that I have seen trailing edges where folks have squeezed them down too much and the radius was actually squeezed flat.
I did a little squeezing and banging on mine to get what I wanted on my plane. It is really surprising how much effect you get from a change that you can't even see you made by looking at it.