Dealt with a lot of this over the years so I'll toss my .02 in as well. One thing that I didn't see mentioned was attention to the geometry of the linkage when using control horns. Always try to keep the distance between the servo arm center and linkage attach point as short as possible and the aileron horn as long as possible. You'll have to use maximum throw available on the servo to make this work. This arrangement gives the servo the mechanical advantage rather than the aileron. However, the best way to insure success is the mass balance method which almost always works.