Well, there is a number of things that take a different amount of time and effort... here are some things that helped me (adjusted for your preferrence to play Medic):
1) If your framerate is low (in 30-40 area), you might want to lower graphics settings in order to get these extra frames. I've experienced it myself in a bit different way (when I upgraded my rig) - when my FPS went up, my actual performance also improved. Never reduce field of view though - it can be the difference between spotting someone and getting blindsided.
2) Pick a couple of map-gametype combinations and learn them - experience often makes the difference between winning and losing a gunfight. Very few people can perform well on every single map, so it's better to identify ones you're doing better on and stick to them, at least initially. When you stick to the map for a longer time, you will start noticing that people prefer using certain spots, spawn in particular areas and so on; this knowledge also involves noticing when the big enemy push is coming (which means that, depending on situation, you can often escape instead of fighting a fight you will badly lose anyway). That will increase your odds of getting a jump on someone.
3) Lean on minimap and your ears - minimap can let you know ahead of time where enemies are; I don't think there is a need to explain why it's a big thing. About ears... listen if there are any footsteps or gunfire around and let the enemies responsible for them mess up and come to you.
4) Stick to your teammates - being near even 2 other people means that 1) there will be two more guns to support you and 2) Enemies might focus on your teammates rather than you.
5) Adjust playstyle to your gun, not the other way around. For example, if you use the Selbstlader 1916, stick to mid-range combat - most of weapons will outgun you on close range. If you have M1907 SL Sweeper, don't try to snipe someone from long distance, because you will probably lose (or at least give away your position).
6) Don't pick fights you have no chance of winning. Do you see a tank rolling towards your area? Are you the only thing between the massive red blob of enemies and one of your flags? Don't play hero - take cover and don't move out of it for a while (or just leg it).
7) Spot - it will result in enemies getting a red icon above them (and on minimap) for few seconds, which means that the chances of your teammates helping out rise.
8) Take note of class of enemy you're attacking - you might want to be more careful when engaging a sniper on range (but your odds of winning in close combat spike), but at the same time attacking an Assault from longer distance generally means that he won't be able to effectively fire back at you (you're probably dead in close combat though).
