Carry over as many TH free passes as possible from previous Treasue Hunt Event.
When new TH event starts hit "Play Free" as soon as possible, even if you don't intend to play immediately. Make sure to play within the 6 hour window and set alarm to take advantage of all future free plays (1 every 6 hours).
If starting out with 10 free passes (the "max"), always try to play enough games to get under the max (9 or less) in order to take advantage of free passes earned in game. Free passes earned do not count if you are already "maxxed out".
Connected with Item 3 above, make sure to anticipate free passes from leveling up...if you currently have 10 passes and your teammate levels up your shared vault, you lose that free pass.
To maximize gems collected, make sure to have access to solved maps. You get 10 points for each leftover move (only up to 3 moves). If you can reach the 2nd target score, it is beneficial even at the expense of using extra moves.
When trying to fill more than 1 vault, choose which vault to add gems to wisely, keeping in mind that if you already have 10 passes, you will lose the free pass earned by leveling up.
PLEASE PLEASE PLEASE Communicate with potential partners BEFORE inviting or accepting them. Important things to know are...Is your partner a "serious" player looking to fill 1 or more vaults? Is your partner a "casual" player just looking to have fun and collect any prizes they can even if they don't fill any vaults? Is your partner looking to fill all 5 vaults needing a "Lucky Pack"? This partner is not going to be a happy camper if you don't provide your fair share of the gems :(
Be a good friend to someone needing 5 vaults. 5 vaults are very hard to fill without using a lot of resources time, bonus rolls, etc. so if you only want to fill 1 vault, partner up with someone needing 5 and let that partner know you will do more than half...that way they can concentrate on their other 4 vaults and save yours for last...You will make a friend for life :))