Post-Activation Potentiation (PAP) increases the number of cross bridges that attach by increasing the sensitivity of contractile proteins to ionized calcium (Baudry and Duchateau. J Appl Physiol. 102: 1394-1401, 2007).
Supramaximal Holds (hold a weight near lockout that’s more [~120% of 1RM is a good guide] than you could ever lift through a full range of motion, thus tricking your nervous system into releasing more neural drive to your muscles) followed by your prescribed set will work.
I've found it to also work after a heavy set, whereby the following set (ideally the last set for that exercise) is lighter. But you'll be able to get more reps than you would if you had used the same weight in a normal training fashion.
You'll often see coaches use it on athletes in the following way: heavy set of squats in the 2-3 rep range, then within 30s do some plyometric leg work. Defranco uses it.
Here's an article detailing that immediate use of the PAP is not needed:
http://articles.elitefts.com/articles/training-articles/some-simple-solutions-to-a-%e2%80%98complex%e2%80%99-problem/
I believe that both immediate "use of PAP" or <=5mins later use of it works to some degree.
Enjoy
