I actually coached a friend in a freeroll the other day and it depends largely on the structure.
if you're playing a tournament that starts deep (200+ big blinds) try to see as many flops as you can early on for 1-3 big blinds. People give a lot of action with just one pair after the flop so you can get paid out well (just be cautious yourself)
this gives you a chance to get ahead of the big blinds before they start rising, and if you miss the flops, no worries, you invested a little.
As for playing big pots, make sure you have strong
hands AJ minimum, but usually medium to big pairs like 99+ and AK. People will happily get all their money in preflop with almost anything, so it's nice to have hands which can have a 70% favorite.
Be patient once the blinds get really big, and hoe to run well in your all-ins.
As the previous posters said too, don't expect too too much because the
odds are against you in fields this big, but the payoff can be quite nice for an investment of 0!