Might be dead obvious but if your drill the holes for the hinges before building wing/stab/fin it is very easy to get perfect alignment between the fixed part and the control surface. I usually drill the holes in the trailing edge then clamp the trailing edge to the control sufface (or stock if it is build up) and drill through the holes I allready drilled in the trailing edge. I use a drill press for this to get things perpendicular. Much easier than for other types of hinges.

Regards
Rcer.