If you wish to return a bow, do so with your back straight and your hands at the sides. The longer and deeper the bow, the more respect that is shown. Bows are often repeated over and over, getting slightly less formal with each iteration. Sometimes a bow and a handshake are combined; if this happens, turn slightly to the left to avoid bumping heads.
Although the few minutes immediately following formal introductions can be a time for nerves to set in, avoid putting your hands into your pockets; doing so shows boredom or lack of interest.