Ive got a tip about medics, dont prioritize heavy's. If the heavy is taking some damage and u see an injured scout or solider or any other class near by, the heavy can usually survive a few seconds with out u on him, take the time to heal ur ally because u never know how helpful that ally can be wile ur attacking, and if the heavy isn’t taking damage, stop wasting time healing him when hes not and heal other people.
Another thing to remember as a medic, u are the only thing between ur target and a spy, so watch ur targets back if you can, most of the time the spy is to quick for you, and if you dont have a mic its almost impossible to warn them before its to late, but also watch for opponents who think they are smarter then you by finding a way behind you, warn ur heavy or what ever target u have, and they will quickly stop that from happening, and if worse comes to worse the needle gun is very effective against people who charge in a straight line at you
Another thing you can attempt to do, is be a diversion, being a medic you are usually the main target. So if u see 4 soldiers shooting at ur heavy, try and get the fire on you so ur heavy, or what ever class u might be healing at that time, has a chance to take them down, because the medigun can only heal so fast, 4 soldiers on a 450 hp heavy are going to win that fight.
One last thing, dont fallow people blindly, if you think its to dangerous for you and a pyro or heavy or solider to rush into enemy base alone, just the 2 of you, dont do it. there’s no reason a medic should die for one guy when he could heal multiple guys and keep a push moving up...
that is all I think