Taking out as much slack as possible before shrinking forms the basis for a good covering technique. The "half point rule" is basically tacking the covering down in places that are halfway between previous tack points. While you continue to add more and more of these points, some of those that you made earlier may loosen as the covering stretches. Those points need to be pulled and retacked.

I would like to recommend a few excellent resources on covering techniques :

1) Tom's technique by Higley
2) Top Flite Monokote video
3) Covering R/C planes by Faye Stilley

If you guys need the links, let me know and I'll post them. Hope this helps