Whenever I'm playing a match I'm usually calmly trying to assess my opponent and see what kind of habits or patterns he follows. Between that I usually mix up my own approach to try to catch them off guard when they try mixing up on me. Heck, I hardly ever pay attention to my character to see what I could do to approach (even more-so since I main Nu) and try to figure out what my opponent will do next.
I suppose the biggest thing that has to be in your mindset is "don't panic" even when your taking a full pressure string, half you heath gets taken out, or you just plain old screw up, you cannot lose your cool. Once you do that, you've already lost. I should know, it happens to me every time I fight a good Haku or Tao. :8/:
Also, don't drop those sexy combos.