There is one advantage that I have learned over long time that not many people can do it well...and it annoys the crap out of everyone when I use panzer
BE UNPREDICTABLE!
Examples:
1) Never stand in one spot too long.
2) Dont follow your team mates around too close. Cover them but move around the map so that you get the best suprise advantage over the enemies.
2) If you are sniping then change positions often because if a sniper doesnt get ya then an airstrike or something else will.
3) Try not to rush out of the spawn nor move along the same path.
4) If youre a panzer...dont rush it...wait for an opportunity and never attack head on unless its a chocke point which you wnt to push the enemy back.
5) In general when using pistols/guns make your strafing unpredictable. If you get into the routine of strafing the same then you will be picked off easily.
6) Sometimes its better to retreat than wait around. Move out of position, regroup and attack from another angle. The enemy wont know what hit them
7) Being medic is fun but being a great medic is even more rewarding. I'm talking about reviving your team mates when in a fire fight. Some players take chances and wait others know that their medic will be there to revive them but what you need to know how to get to your team mates without dying. You rez your amte and you die...chances are you will get rezzed up but what is a cunning technique is reviving them and going behind them, the invulnerability (for 3 seconds or so) act as a shield so while the enemy is frantically spraying bullets you can hide and then attack with your mate...so sometimes it is better to rush and revive your mate head on.
8) Using grenades is also effective and can deter the enemy. Chuck a nade in one direction and run around the enemy from a different angle. In most cases they will take the liniar path while you wait for them from the side.
9) When in a dog fight...use cover to yur advantage. Move around it and make your enemy think where you will be. Alwasy try and have your back to the wall.
10) Practice practise and more practise. Get to know the map, the surrounding, learn to time your attack, learn where enemies are/could be and your team mates. Timing is crucial but being unpredictable is one of the most important things in online multiplayer gaming.
Good Luck
The problem why people are predictable and so many times I have know where to shoot my panzer (and afcourse get the timing right) is becuase I can predict their movement to some extend. The problem is you have to know your map well, the surrounding and timing is crucial. You can learn all these things and become good at smg (gun) then you can become a great player.