Try to learn how to relax and spar/move smoothly. You can train like anything and get really fit, but sparring is one of the most tiring things you will ever do. If you watch others in your gym, you will see some people seem to get tired more quickly than others (but they are just as fit, as you can check out during training).

A lot of people get very tense in the shoulders and clench their fists too tightly - I know it sounds odd, but I think the gift of relaxation is a greater gift than immediate one-punch power.

Oh, and good luck - make sure you enjoy it!