1. Get the idea out of your head that JJ is a hand where you're going to be making tons of money every time you get it.
2. Analyze it. Probably alittle less than half the time you get to see a flop you are going to see an A, K or Q. So at that point you have to play it as if you've hit second pair, or third pair if you have two of them come off. If you had JT and flop came A-J-3, how would you play it?
3. When you bet or 3 bet pre, understand that unlike with QQ or KK, you are going to have a few more
hands that have two over cards that you are going to be up against. KQ, AQ, AK, turning that match up into a coin flip situation. Play it accordingly if you meet strong resistance.
There are so many variables that you can't account for that asking "how do I play this hand" just won't get you all the information. Find a spot where you lost with JJ, and analyze it. I bet you that find a spot in most of them where you simply over valued your hand.