The early part of a freeroll has many people who will go all in or call an all in with nothing.
In my opinion, you have a few options:
a) Join the bandwagon. Make your early gamble. If it pays off, you then have a nice stack that will give you a better chance later. If you bust, well it has cost you nothing and you've barely wasted much time.
NOTE: Choose a point to stop. Your luck will not hold out forever. Be thankful for your early windfall, but change to one of the other options after a short while.
b) Avoid the frenzy. Walk away and leave it to sit out whilst the blinds are low and people are treating it like a lottery. Come back when you still have about 2/3 your initial chipstack and try playing from that point (after play has settled down somewhat). That way you are not wasting your time watching the chaos.
c) Capitalise. Stay and play, but keep in mind that hands can escallate quickly. Watch the tempo of the table to see whether it is likely to have pre-flop all-ins, post-flop all-ins, or simply standard small pots, and play to that.
* If pre-flop all-ins are rife, play only premium hands. You can lead with an all in that you expect at least one or two callers for, or you can opt for a limp or small (standard) bet that you expect someone to try to force you out and surprize them by calling/reraising instead.
* If post-flop all-ins are the go, then a few random limps can be good. However fold unless you hit hard. A good hit on the flop can pay bigtime.
* Alternatively, the table may simply play a normal game. In which case you can play as if it weren't a freeroll. Or you could stir it up with an occasional wild bet of your own if you think your tablemates are very timid. Just dont go overboard.
Mid tournament, most of the lotto players have busted or settled down, so you can play a normal game for the most part. However be cautious of those that decide they need to go and start wildly throwing their chips about. Sometimes this is just a ruse to get you to call their monster had with a mediocre hand. Othertimes it is genuine, but still proves disruptive to the play. By this stage you have likely invested considerable time into this game, and thus should be less inclined to gamble it all on a draw. However, if you are dealt a monster at the right time, or happen to be shortstacked and really need a windfall anyway, then sometimes these players can be just what you need.
Late tournament, everyone has made a considerable investment (of time), and thus the fact that it is a freeroll is less apparent. However, check for absent players. Since it is a freeroll, there are likely players sitting out (for whatever reason) sometimes (but not often) even on the final table. Play aggressively when an absent player is in the blinds, because you know they'll fold and their chips are just padding the pot. Others may not be so observant, so you can pick up quite a few free small pots this way.
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One word or warning
Be careful to only use freeroll tactics in a freeroll. I've occasionally forgotten that I was playing a paid entry tournament and lost my entry on a gamble I never should have taken. So, if playing to the type of game you are in, make sure you know what type it is.