1. Practice - don't need to say much about this. You can remain calm under pressure if you have a lot of practice. I include area/gear knowledge in this as well. Also knowledge about CF mechanics and the various classes/races.
2. Self-awareness - you must know your own style and strengths/weaknesses as a player. If you can't keep track of the various moves you can do in combat, don't play an invoker. Play a simple melee lagging type. If you can't track affects, don't play a transmuter. If you like taking some risks, don't play an AP.
3. Thinking Probabilistically - this is the hardest, and it takes practice, some minimal level of intelligence, and quick-thinking. Good poker players can do this very well. You should always be making decisions that minimise your chance of death and maximise your chance of killing. Of course if you have some risk appetite, feel free to risk deaths to get kills. At some point you need to be willing to risk deaths to get kills. Your desired kill/death ratio changes with your skill. If it's 1-1, then as a skilled player you will play "balls to the wall", and even then you'd kill much more than you die (cf: Marcus / Flipside Oreo).
Some examples of probabilistic thinking: You're fighting a basher as an easily-bashed player. His probability of sealing the kill on you if the fight swings his way, is significant. Your probability is not, unless you have some good kill-sealing skill like Sleep, Entwine, trip (if he's not flying), other lag options. Don't fight him unless you overpower him. The whole point of playing bashers is that you have the OPTION of locking down and thus scoring the kill. Naturally you should not expect to be as "strong" on average as non-bashers, like Invokers, Paladins, dex warriors. Similarly, if you're facing a basher who outmelees you, just get out or prep hard enough to overcome him. When I play bashers I'm happy to fight people "stronger" than me because I just need one chance to catch them off-guard, and I have a significant probability of a kill. For example I killed Lezra (Scion Chancellor alligator with the Scepter) as Humbert because he was out of form and anti-bash fell.
Same deal goes for Sleep, or Assassinate.
Another form of probabilistic thinking comes from "sizing up" the skill of your opponent. For example by glancing at their gear and watching their commands in fights, you can tell if they're skilled or not. This ties into self-awareness - you should know how skilled you are. Then adjust your tactics accordingly. However, skilled players will sometimes pretend to be less skilled, or less threatening. Personally I do that sometimes by wielding very weak weapons at the start, or non-spec weapons, or using low damage spells. I.e. on a transmuter I sometimes do accelerate, petrify flesh, soften, mental jolt, muscular lethargy, before I actually aim for the kill. On an invoker - flare, web, grease, rain of stone, quicksand, conglaciation, immolation, before dumping the big damage spells on them.
