If you play with your hands, or tend to play with items when you are nervous, then do not allow your hands to touch. You can gently hold your wrist when in conversation. This will help reduce the temptation of wanting to play with your hands.
Do not clasp or hold your hands with a fist, this might make you appear closed off, tense, or angry. Instead, have them lie on your leg or arm spread hands down. But don’t be so stiff that it is unnatural. Video tape yourself. You want to see how you sit naturally and what message it is sending. If you are doing anything that I mentioned above, then you need to find some position with your hands that are comfortable for you while communicating that you are open and trusting.