The above is the correct proceedure, but you want to lift the plane several times and see which way it tilts. If it tilts the same way each time, add a few weights to the wingtip (the side that keeps going up). Repeat this proceedure until the plane either stays level, or tilts in either direction. Then, permenently attach the weights.

I like to use something like "Split Shots" as weights, then when it balances, remove 1 or 2 (depending on their size), put a small hole in the wing, forward of the spar where the wing is sheeted (and therefore encased in balsa) and then drop in the weights with a little CA or epoxy to hold them in place. guesstimate the amount of epoxy to be about the same weight as the weight of the splitshots you removed. Then apply covering over the hole.