first remove control horns from surface.
you can do the next bit which way you want, depends on how you like it... but....
lay the surface upsidedown on top of the wing or fin or tailplane, ( oh yer... this is for top hinging btw... ) move the surface untill its flat with the rear edge of the w/f/t
then run the tape along the joint. fold the surface down into the normal poistion and past till the sanded bit is flat against the w/f/t back edge, then tape the top.
sometimes its easier to do this the other way around.
i dont bother with just tape for center hinging, coz if you think about it.. theres nothing to stop the tape from comming away till its just from the TE of the w/f/t and LE of surface leaving a gap between.