When standing, trained interpreters keep their hands at their sides or poised to take notes. When seated, their hands are on the table in front of them, in their lap or poised to take notes. Experienced interpreters know that fidgeting with their hands or putting their hands in their pockets looks unprofessional.
Most interpreters carry a pen and notepad with them on assignments. In addition to being ready to take notes if necessary, this keeps you from fidgeting.