My routine is:
1. Sand the area
2. apply glue using the tube tip to spread it (no fingers.)
3. wait LOOONG time for glue to dry
4. remove backing from patch and carefully place over hole.
5. there's no second tries for placement; if you mess up, start over now!
6. firmly roll/press the patch into the glue and let sit another LOOOONG time.
7. after a zillion years, it's OK to remove the plastic from the other side of the patch, but usually I leave it on and reassemble the tire.