another trick is to be sure to sand the leading edge very carefully, making extra sure that it is round and the radius is as large as possible. You can let the radius tighten up near the wing root then the root will stall B4 the tip. Also, when covering, make the outside half of the wing all one color with no trim strips, letters, or other roughness that would trip the boundary layer.

Another thing: wipe off all the hanger dust before you fly it...that's why they de-ice airliners before they take off.