Trying stuff out. By all means feel free to experiment with new techniques while you play TFC, try and emulate the players that you see doing well and also learn from the mistakes of others. Do NOT use a full up public server as a place to test out your latest binds or spray paint image, or to spend all match trying to rocket jump up to the roof in the epicenter respawn. If you want to try these things, go and find an empty server where you wont disrupt 17 other players trying to play a game. If you can't find an empty server, create your own LAN game to practice that kind of thing on.
Many people have a tendency to blame something else when something goes wrong.
It's human nature. It's also a pain in the neck to listen to someone constantly whine and blame everything but themselves. The same goes for blaming other players, their will be a wide variety of different skill levels on any server, if one particular player constantly kills you, don't accuse him of cheating or of only killing you because he has a fast net connection. It makes you look like a bad loser, either find try to avoid the good player altogether, or keep trying different classes and techniques until you find a way past him. If he still seems invincible, try spectating him for a while, you will learn some valuable skills by just watching good players.