Solid advice - but having chat off isn't an issue on ACR - the damn chat doesn't work! Unfortunately
Solid advice from all the above quoted posters.
Just to reiterate and add - early on (first 20-30 minutes) only call shoves with premium hands QQ+ Half the field is shoving any Ace, any pocket pair 22+, and any two broadway cards.
The only exception I will make to this rule is if I have a strong Ace in the blinds and have one LP shove.
TAKE COPIOUS NOTES.

The reg freerollers have EXTREME tendencies and are easy to outplay once you have learned what they do every time they get an Ace.
Shoving all-in is a donk move without premium holdings - however it is also used strategically to intimidate. Although this tactic (imo) is totally reckless - it works. I don't employ it without having +EV vs the table/opponents, however after learning the player tendencies - making calls vs certain opponents is a lot easier.
I use min-raise and punish limpers with 3bets if I have the stack to do so.
Limpers are playing rag Ace, any two suited or any single broadway from any position.
Don't worry about trappers until the field falls below 70-80 players.
There will always be 1-2 luckboxes that have 6-8x average stack that you have witnessed shoving with 9/3 s and pocket 33s and decimating premium holdings. Take advantage of those players - they are great at giving away chips - after they have lucked into a large stack.
Don't get flustered if you loose early - A LOT OF PLAYERS rely exclusively on luck playing these events - they can be dominated by playing strong later - but busting early is just part of the game.
Strongly agree with bellicoso regarding tedius boredom. It's good to have 1-2 other events open at the same time, although I really don't experience this as I'm always looking for edges by watching how players play.
You should notice - certain players play the same in CC freerolls as they do in those OD freerolls. Take notes - those players can be a real good source of chips.
This is the way
I have been sending emails to ACR periodically to request they re-introduce the freeroll leader board - to make them more meaningful. There used to be a leader board - where the top 10 qualified for a buyin event each week, and the top finisher of the week qualified for a much more lucrative event (sit n crush?).
It is unfortunate they discontinued the freeroll leader board - because now there is barely any incentive to play them.
I think if I keep pestering them - they will relent and reinstate it.