Thinking of competing? Here are a few things to consider before you do.
1) Pacing. The difference between rolling on the mats and going into a comp arena is astonishing. In a comp, people don't warm into a roll, they go 100% immediately which may burn most of the energy out of one or both of you within the first 90 seconds. Keeping your breathing under control and only being explosive when necessary will help mitigate any excessive bleeding of energy.
2) There is only one tap. In a roll we try to respect our training partners by not only keeping an added measure of control when applying submissions, but also by communicating our weaknesses and what to watch out for. This will not happen at a comp. If someone sees weakness, they will pursue it. If they try a submission, they will wrench it. If you feel trapped and need to tap, do not hesitate to do so as this will protect you. Likewise, if you feel someone tap, do not continue to wrench!
3) Timing. Competition day can be long. Depending on how many categories you've signed up for or want to watch (Gi, Nogi or Absolutes), your day could be as long as 10 hours plus travel time. After you weigh in, if you have plenty of time before your first match be sure to eat, hydrate and relax as best you can (don't forget to have a toilet break). Once you get within 15 minutes of your match be sure to warm up and get as close to the intensity of the match without wearing yourself out. There may be slightly longer or shorter pauses between your matches then you'd suspect. Try to keep warm and hydrated.
Finally, I will say this. Enjoy yourself and be a good sport.