JJ is probably the most difficult hand to play in No Limit Hold Em Poker. The problem lies in the fact that anyone with AK AQ or AA KK QQ is going to call or reraise any thing you bet. Obviously your behind the last 3, but even the first 2 are 50/50 to outdraw you, and if they do you are way behind. Also, many people have a hard time of letting go of Ax and they may catch that A that beats you.
What I do with JJ is raise 5or 6 times the BB. As long as I'm not reraised, I'm probably not facing AA KK or QQ. Any flop without an overcard is good and I can bet big and should take the pot. See an overcard and I treat my JJ as if it was pocket twos that missed the flop. The reason most people lose with JJ is they go allin preflop, and now you can't get off it even if you wanted to, or they keep betting after the flop comes with an overcard.
Even if you play it right, you can still lose (but that can be said about any two hole cards) but play it wrong and you WILL lose.