JJ is a tricky hand to play and if any over-cards appear on the flop, you're sunk.
This is how I tend to play JJ in a tournament (might be appropriate for cash games as well)
:
First to open (from any position):
Std PFR to 3-5X BB
In a limped pot:
MP: Makes the appropriate 4-bet to 3XBB + (1BB for each limper) [reduce depending on stake sizes]
LP: 3-bet to 4-6XBB (kill off all the junk
hands and try to see a flop)
In a raised pot:
This is where everything can either go perfectly or completely haywire.
If your opponent is a loose player. You might want to 4 bet to 2.5X the original raise to see where you're at. If he flat calls, he's likely holding a drawing hand. Let's face it, if you old the overpair to a dry flop there is no way you are getting away from it: just shove and hope to take the pot down immediately.
If your opponent is a tight player that rarely if ever 3-bets. Make the 4-bet. If he comes over the top of you, just kiss your jacks goodbye and muck. If you sense that it might be AK, decided if you want to take the flip.