When I say pocket jacks, I'm referring to two Jacks, pre-flop, in Texas Hold'em. This is the fifth best hand in Texas Hold'em and in general, I would say you should never fold this hand (especially in limit hold'em). But it is definitely one of those hands to be careful with.
Pocket Jacks is especially tricky for one main reason. The most important thing to realize about this hand is that if you raise too big with this hand, normally the only people who will call you are people who can beat you. Therefore, I would suggest a small raise or possibly a reraise preflop with this hand.
Before the flop, successful Texas Hold'em strategy is pretty straightforward using your top ten hand strategy. In general, you should raise every time you have a top ten hand and you should fold the rest of your hands to any raise. It is because of this basic strategy of Texas Hold'em, that this raise with pocket jacks is especially important.
Raise too big and get a caller, then you are starting out way behind. Don't raise big enough and someone with a lesser hand will catch up with you on the flop and then you will have no choice but to fold.
Consider this scenario. You raise a small amount on the button with pocket jacks and you get two callers. The flop comes and brings an Ace (and no jacks), the person in the first position bets half the pot. How can you consider calling a bet of this size with only an under-pair? The fact is, you can't.
A larger bet would have scared away someone with say, Ace-Six as their pocket cards.
Probably the best way to avoid misplaying this hand is to have a good read on your opponents. This read will enable you to place an appropriate bet, ensuring successful play of pocket jacks.