First and foremost, I suggest you train regularly for about two months before the particular tournament that you seek to enter. You can always jump in and be successful, but you will have much more success when you are adequately prepared. If you seek to be at the top of the top in this sport, you will have to train almost full-time according to Roger Gracie (who currently has the record for most black belt world titles). The competitions and numbers are definitely growing, so it’s only a matter of time before the competition gets even stiffer.
I also recommend a healthy diet if you seek to compete. I will not get into the finer details of what I think is the best way to lose weight or if weight loss is necessary, but often people will cut more weight than they can handle prior to a tournament and it may affect them. Discipline is crucial when it comes to dieting and making a proper training regimen.
Another suggestion is to make sure you warm up prior to your matches. I think warming up is much better than going into a match totally cold. There is a a world-class wrestler who would often have a warm up match with a teammate about thirty minutes prior to competition so that he could feel warm before he even stepped on the competition mat. How you warm up is solely up to you.
Most of these tournaments have your specific weight class and division on one mat. Then more than likely you will enter what is called a bracket and you will work your way through your opponents continuously until your division is done and a winner is declared.
When you become a more seasoned competitor, you may also begin to study potential opponents on YouTube and other various video outlets.
If you win, be humble, and if you lose, be gracious. Do not be that guy cursing at the referee; please do not lower yourself to this. There will be calls may not like, but a competition is something you chose to enter and the risks of losing and human imperfection are inherently there. I am not saying do not ever contest a call—just have some decency when doing so. Also be prepared, be on weight, arrive in shape. BRAZILIAN JIU-JITSU is a contact sport and it can be very dangerous, especially if you are ill prepared or come in with an injury.
Here are the Rules again: