Racing a duathlon is different than racing a tri.  First, a run leads it off.  Seriously, there are ways to race a du that go beyond leaving the wetsuit at home.

Warm up more than in a triathlon.  You'll need to run easy for 10-15 minutes with several fast accelerations to race pace to get the blood flow moving and ignite the neuromuscular timing needed to start out fast.  The race will start fast, so go hard off the start and get into a good position.  Don't overdo it, however.  Settle into a sustainable pace, a little easier than you expect to go for the entire race.  Relax in T1 and make sure you set your shoes up so that you can find them in T2.  Ride hard, as in a triathlon, but relax a bit in the beginning.  Pick it up slightly at the half-way point and hold to the finish.  Relax a bit in the final 1-2 miles of the bike and spin in a high gear to anticipate the run.  In T2 ensure you get all your run gear, and run out at a solid pace for the race.  Your legs will be somewhat heavier leaving T2 than in a triathlon due to having already run.  This feeling will only last the first mile, so push through and run on 'heart.'

Make it happen.  And have fun.