Listen to what Day had to say and make good apps.

It's also a good idea to find the clan and befriend them before joining.
To find a clan in-game, go into Toribash and type "/rf" (refresh) and "/sa 'clan name'" (search). Start by saying hi and don't jump to the "can I join?"-part.

This way they get to know you on a better level, and your chance of joining will be much higher.

Make sure you join the right clan for you, as the clan you're in will be the clan you play with most of the time.

Good luck.