Rubbing the palms together often communicates positive expectations – you may see a gambler doing this with dice in the hope of winning. You may also notice that a salesperson could do this in expectation of making a sale. This is also common with someone with cold hands! Anxiety is more often identified with more of a “wringing” of the hands, rolling / clasping them rather than just rubbing the palms together.
In saying this, each person is different, and not one interpretation is universal.