Sometimes you don't even know your own
tells at live games, it's recommended to get settled into a local club game once a week, become friends with a few and discuss this stuff. in my experience it the pressure of tough spots becomes the norm, the sweats no longer happen etc because your used to the spots (although you take some time off like a couple of months, these will come back for a small brief time until your comfortable again)
with that being safe, what CRStals said above, play every hand the same, same posture, timing etc will help.