All too often in a class-based multiplayer game I see players utilizing the Medic wrong. I tend to play as the Medic religiously in multiplayer games and I too have found myself making the dumbest of dumb mistakes on the battlefield--be it Bad Company 2 or Killzone 3.
The most important rule all aspiring Medics should know is that your class is not designed to be a rusher. Have you ever noticed that your gun is roughly twice the size than that of say, an Engineer or Scout class? You know, the ones that are meant to be in the heat of every battle? That's because you, as the Medic, are specifically constructed to give support fire to the rest of the team, and just squeeze that trigger to no end while sitting in the back somewhere. You have about 100 bullets in your magazine, and the purpose is to spread them across your sightline so that the rushers can pursue an objective.
A lot of times I see Medics completely ignoring wounded teammates just to storm a building and rack up his or her kill/death ratio; these people probably think they are doing a good job too.
WRONG!
Another big problem that's become somewhat of an epidemic among Medics everywhere is that once they see the icon of a dead soldier, the Medic revives them no matter what. I'm sure most of you can attest to this scenario as well; you're in a narrow hallway, get shot and killed, and then a few seconds later you are revived by a Medic just to be shot and killed again a second later. This is not good Medic performance whatsoever.
If you see a dead teammate, you can't assume that the threat has immediately come and gone. Check your surroundings, make sure everything is clear, and then do your best to make it to the one you are trying to aid. It won't do any good for you to revive a recently killed soldier in front of an enemy. Also, you are not a one-man revive team, so you shouldn't risk your life to tread across the map to try and save one dead teammate. Chances are once you get there that player will have respawned, and you could've used that time to save closer members.
Just think wisely.
Oh, and lastly, we need more people playing as Medics. I see far too many people playing as a Sniper/Recon class or straight up Assault. In most class-based shooters, kills mean diddly-squat. Hunker down, play smart, and play your class.