Now that Team Fortress 2 supports the Oculus Rift, you might be tempted to jump right in with the headset strapped to your face — but the Oculus Rift user guide on the game's official wiki advises a more gradual approach.
Enabling Rift support in Team Fortress 2 takes a bit of doing but is relatively simple: You'll have to add "-vr" to the command line launch options and enable the developer console. The wiki also recommends calibrating your inter-pupillary distance — the distance between the pupils of your eyes — for the best experience.
You may have to limit the length of your initial sessions playing Team Fortress 2 with the Rift, according to the wiki, because "[virtual reality] is awesome and immersive, but it can't fool your senses all the time." The wiki advises users to play only for 10 minutes at a time until they get their "VR legs," and suggests starting with slower characters like the Heavy or the Medic, since the faster classes "can produce particularly intense experiences in VR" — and motion sickness.
Valve announced Rift support in Team Fortress 2 earlier this week.