I have done a few Iron Butt certificate rides. I never did a BunBurner 1500, but I have done a BunBurner Gold.
My tips are probably the ones you hear over and over again:
* MOST IMPORTANT: Know when to stop. My Iron Butt Heroes (tm) are the people who stayed safe and decided to call off the ride. Some of my friends quit when they were less than an hour from their goal.
* Keep your stops as brief as possible. Strive to keep them as close to five minutes as you can.
* Watch hydration, body temperature, nourishment, and rest. You must drink plenty of fluids while you are riding, not just at stops. Know how to stay cool in summer and warm in winter. Know the signs of dehydration, heat exhaustion, hypothermia, fatigue, etc.
* Get lots of miles early to give yourself a nice time cushion. If you can knock off the first 1000 miles in 16-18 hours, then you will have plenty of time to get the remaining 500 miles after a good rest.
* ALSO VERY IMPORTANT: Have fun!