Freerolls are tough simply due to the number of players who will chuck all-in on shit hands. I’ve won a couple with 800+ players and usually make the money but for such a long period of play unless you hit the top few spots the returns are usually fairly crap and not worth the hassle.
Best advice for a freeroll is to simply sit tight for the first couple of hours while the fools chuck their cash about only play solid high hands. Once people start to settle in then is the time to start playing a little more aggressively and building a good stack.
I can go at least an hour at the start of a freeroll before actually playing a hand.
Good article here, which is worth a read but at the end of the day develop your own style and make sure you can adjust to the table your at:
http://www.totalgambler.com/poker/strategy/5394/poker_stack_management.html