Obviously there's a few ways to do it, but I do mine the following way.

I first cover the wing normally and allow about 1/4" of covering to overhang the wing tip. I then take a razor blade and cut slits in the overhanging covering every 1/4" or so around the leading edge bend so it will lay down without wrinkling. If there is a sharp bend area such as the leading edge I'll put the cuts closer together (every 1/8" or so) and for long gradual bends I'll put them every couple inches.

What you end up with is a 1/4" overlap onto your wing tip and then cut out a piece of covering to iron over the wingtip that overlaps the seams and you have a nice clean wing tip.
I don't have any good pictures, but on the White wing you can see the overlap at the wing tip before I put the covering cap over it, and the other is the finished product on my SSE.

I think the heat and stretch method would be cleaner but does take a little practice to get right.

Good luck

**edit**
Found another picture with the overhang before I cut it and ironed it down.