- 1) Design some levels. Yes believe it or not, to have a competition, you need to have built the levels. Yet again and again, people are starting the competitions with out them.
2) State the scoring method. There are plenty of examples out there. Pick one - or build your own - just do it. And for those using OfficiallyHaphazards often cut-n-pasted rules or something else cut-n-pasted, try proofreading it. For example, cut and paste a copy that doesn't say that lightning is not included in the calculator - it is. Some sample rulesets can be found HERE
3) Give clear beginning and ending times to each round. Yes, people need to know how much time they have to tweak. "12:30 PM EST 12/31" - gee that was tough. Don't pick some date a month out, 36-48 hours is usually enough - but can vary depending on how many rounds you have.
Once you have established the above
- 4) STICK WITH IT. Don't change the levels 1/2 way through - people have probably already started working on them. Don't change the deadline because you haven't gotten any submissions 20 hours before the deadline, some people tweak until the last minute. Don't change the scoring - don't like it? run a new comp later.
A few parting thoughts:
- You don't need to bump your thread every 2 hours. Once a day is enough if others aren't doing it already. More than that you just look like an attention lady of the night.
- Don't expect 100 people to sign up. 5 to 10 people is the norm - unless you are actually any good at running competitions (and by the way, unless you are jtbowden or OfficiallyHaphazard, you probably aren't), in which case you might get 20 people.
- One concurrent competition is enough. If you want to run another, wait until your current P.O.S. is over.
Stick with these few basic principles, and people will have fun. If they have fun, they will likely join another tournament you host.
200 
!
IMO, every contraption is extremely conditional because you're trying to get the specific goal piece on that specific level, to the specific goal area. 
