Park Tools does a pretty good job of describing how to properly patch a tire with all of its products; the VP-1 kit is a "real" patch kit that relies on the vulcanization process for bonding the patch to the tube:
http://www.parktool.com/repair_help/FAQGP2.shtml

Most folks who can't get a patch to hold make the following mistakes:

1. Applying the patch before the "glue" dries. The key is, it's not really glue. What you're applying is a self-vulcanizing fluid that causes a chemical change to the butyl rubber inner tube's surface. It only takes a thin film of the fluid and the fluid must be dry before applying the patch to the tube. When the patch is pressed against the treated surface of the tube the two materials bond to create an airtight seal.

2. Not getting enough activator on the tube (it must cover an area that is larger than the patch)

3. Not doing an adequate job of scuffing the tube.