As for revive coins, they are relatively expensive. Usually players only use them when the team gets wiped out or when a very powerful teammate dies. Since the number of coins required for revival increases with the number of times you use them on a specific player, you should probably not use them on your teammates when it costs higher than three coins. Instead, ensure your own survival and use the coins on yourself when needed. You can get a short period of invincibility after you respawn as well.