There are a few ways to play freerolls, at least in my opinion and it's all based on the number of entrants into the tournament and the frequency of the tournaments.
I started on UB, there were freerolls almost every hour with 4000+ people in them. Stars now with their 10,000+ person freerolls, even Full Tilt with their 2700 person freerolls. Those freerolls require a different type of play to make it worth your time.
Large freerolls, figure out where you need to be to get "in the money", whatever that means. Some sites it's a round 1, top 50, some sites give out $.10 and up, some sites only pay a small number of entrants. First hand is critical, it's an every hour deal in most cases so why worry? If any other player goes all in, follow suit. Never let anyone bluff you off a hand because it just doesn't matter. Once you get past the first hour and 2/3 of the players are gone, then it's time to actually play poker.
Midrange freerolls, it depends on the payouts. If it's a small payout, go for it exactly as described above. If it's a larger payout just play the top 9 hands the first hour, then loosen up.
Smaller freerolls play normal poker but don't let people force you off a good preflop hand by their all in bets on the first couple of hands. I saw someone advocate even folding AA, that's just stupid. Play poker like you recognize how good a starting hand is, sure you might lose to an all in 72os but over the long term the probabilities will favor you.
I've won 4 of those 12,000 Stars freerolls, back when I was just starting and didn't realize what a waste of time that was. I still have 3 tickets for round 2 games, I can never remember to use them. On UB I've won the $500 bonus dollar tournament twice and final tabled it 2 more times, also won the TEC daily and weekly ones. Note that when I say "won" in some cases it means I made the top 50 to go to next round. I've won a 2 or 3 of the CC freerolls as well as 2 from other forums. This strategy works for me, maybe it's not your thing but it's how I approach any freeroll I play in.