All eating competitions have some common rules. These can be about how you can eat and what will be considered as consumed, what will not be and so forth. Make yourself at home with these and you should have a basic idea about what to do when you enter the competition.
Every competition has a rule book. Get a hold of it and read it so that you can understand that what are the rules of the given competition. Meet the people who are organising the event and seek their help in this regard.
If there is no written material available, they can explain the rules to you which is going to be quite helpful as well.
If you are new to these competitions, it is also not a bad idea to get in touch with other contestants who frequently take part at these events. They will be able to explain to you the rules in detail and will be able to pin point finer details that may otherwise be missed.
You can meet them in person or discuss with them online. You are bound to find some on internet forums which can be great for you to understand better.
Start with smaller competitions at a local level and you will start gaining experience of not only participating in the events but also the rules. Nothing beats experience and the same golden rule applies here.
Once you are used to the competitions and know the rules, you can take a part in bigger competitions and show your food munching skills to the world.