I started playing online a few months back with the intention of NEVER depositing and building my bankroll by entering freerolls and then rolling that up at ring tables and SnG's so I'm used to freerolls and the maniac play there.
Whilst I in no way claim to be an expert I am now building a healthy free bankroll of cash and player points.
My strategy for playing the freerolls is to play tight and be VERY patient, play virtually the entire tourney using a short stack strategy, loosen up a bit if you start to build a decent stack but be ever mindful that the majority of players are relying on luck and not strategy or game play.
As the other posters have advised keep your head down early doors as there will be all ins flying around left right and centre, don't be tempted to join in unless you have AA, KK or QQ (preferably on suit) or AKs, and only do so if you can accept being taken down by 2 pairs 2’s & 7’s.
Avoid being the first to go all in, unless you are very short stacked or you have the chip bully at the table and they have laid down a large bet or raise. If I have decent stack I will generally call or check pocket aces and depending on the flop then look to raise and try to draw maximum value from the pot. Throwing all in should in normal play scare of some speculative hands but this is freeroll and anything can and will happen.
Crazy raises are the other thing to watch for and there will usually be a few callers so try not to get dragged in unless you have the cards to take it all the way.
At the beginning when the blinds are low and your stack relatively high limp in to see the flop if you get the chance with even speculative hands, there are a lot of "call stations" and that 7,8o in your hand can suddenly become a straight or 2 pair on the flop and that 30 chip limp can soon become profitable.
Be aware of "dead players", a large percentage of players who enter a freeroll don't even both playing it, or log in late, so be aware of which players aren't active and there position relative to you. Its not unusual to actually find yourself playing heads up as the rest of the table is dead.
Take good notice of what players are prepared to run with, most hands will reach showdown so observe their hole cards and see why they were prepared throw in or match that 300 chip pre-flop raise.
You will find yourself being moved to other tables frequently, take your time at the new table to adjust, allow a few hands to observe before joining the action.
Even in the early stages you will find a "chip bully" at your table, they will have gone all in on first hand and doubled if not tripled up and there after try to raise everyone in to folding on subsequent hands. Be patient, the chip bully is your friend, they are a "cash cow", just bide your time and you'll get the chance to milk them.
Be aware of your position in the tourney, don't panic if you find yourself near the bottom of the pile, its a marathon not a sprint, when the bubble approaches most will "draw their horns in" if you’re low stacked use this opportunity to push pre-flop when you get the chance, most players won’t risk “gambling” at this stage and will be happy to ride their stack through the bubble.
Depending on how many players the bubble leaves there is usually a resumption of frantic play which usually sees a few casualties, so again be prepared to ride this out, you can gain a couple of placings by doing nothing at this stage. If you make the final table good luck, this is all in territory again, play it tight but don’t be afraid to go for it if you have the opportunity.
I hope this is of some use and hope that a few of the better players here can tweak the holes in my strategy.