When you are playing against a chip leader, first consider where he is sat relative to you. If he is sat to your right, acting before you, this can be good because in tournaments, chips tend to flow to the left. You get to choose what pots you want to play with the big stack giving you very good implied
odds. Playing low pocket pairs go up in value because hitting a set is strong and disguised, so you can expect to get paid off or double up even. You want to be looking for more opportunities to trap.
When acting before the big stack, you need to be more selective with the hands you play. Try not to get sucked into marginal hands that have little/no outs to outdraw in case you get sucked into a big pot that you might not be able to get away from. Play more hands with stack sizes similar to yours or smaller, just be careful looking at the effective stack for each hand. Smaller stacks may be prone to shove at any time, so try to get involved when you can afford to take the chance to put somebody out of the game.