One strategy would be at the beginning of a freeroll to play only the very strong
hands like QQ, KK, AA and AK and raise them high before the flop. At least I often get in the money with this strategy. Since the blinds in a normal freeroll often rise quickly, you also need a lot of luck towards the end of a tournament, because often only all in or fold is possible.
A strategy would also be to become a Platinum member and play these
freerolls. There, the quality of the players is much better and it is also only a small number of players who participate.
The chance to win there once is not so bad as a solid poker player.