A few things I've learned... the hard way:

1. It's better to carry a spare inner tube and, if I get a flat while riding, to swap the tube, ride on, and fix the other one later on, at home.
2. After waiting for the glue (vulcanizing fluid) to dry -- and I mean waiting the full seven minutes -- I apply the patch and clamp it under moderate pressure, in a vise, for thirty minutes.
3. Once I release the newly-patched inner tube from the vise and peel off the plastic "cover", let it cure for 24 hours, before testing and using it.

These might seem "over the top", but they've proved to be true. Of course, YMMV.