1) Don't Pocket
2) Don't use slot1
3) Prioritize people who haven't taken damage in a while; they heal at 3x the rate of in-combat patients
4) When running away, crouch-jump constantly so that explosions will boost you
5) Run away, back up, or retreat if you think you are in immanent danger. Leave the melee attacks to the more experienced Medics.
6) Abandon your patient if he is putting you in danger or unable to protect you
7) Look behind and around you constantly; check for spies while healing.
8) If you're not healing someone, be running to find someone to heal
9) You can't save everyone
10) Don't hold ubers longer than you have to
11) Once someone reaches 150% overheal, drop them and find someone else to heal. When the group is overhealed, switch back and forth between patients to top them up.