I think that one of the main things, when you're organizing a tournament, is to be realistic of what you expect from the tournament.

Some things you need to take into account:

Amount of potential players: For example, if it's a temporal tournament, then expect a larger amount of signups than with a long-standing tournament (people then don't feel dedicated to keep going to something that they may not like) . Do you necessarily want to host a big tournament? Do you want to micro-manage several rooms or do you want to just host a 12 player tourney? Do you need help with this?

All of the things that could go wrong: Arguments from hacking, to cheating, to sandbagging, to track selection. You need to have your mind made up as to how you're going to tackle these details. You need clear-cut rules that people can understand, and clear-cut consequences if these rules are broken. Also, you have to be fairly absolute with these. You can't punish somebody for breaking a rule and then letting another person go scot-free.

Making your tournament unique: There are plenty of 'pro rooms', there's already a clan league, you need to come up with something original yet not entirely bizarre to scare off people. If you think you have a great idea, go with it. If it doesn't work out, then at least you tried. Try to use the game to the maximum :).

Concluding your tournament: If it's temporal, then what is the prize of the tournament? What makes your tournament worth playing through? If it's long-standing then how are people rewarded for participating in the tournament? Are there going to be special events?