6 Rules for Successful Sales Incentive Contest

What are your rules for a successful sales incentive contest?
There are six main things to remember:

It must be fair to all salespeople, from the 10-year veteran to the first year rookie.
The rules must be written out and completely understood by all.
It should use a fun and appropriate theme.
All results must be reported on time.
All prizes must be rewarded on a timely manner and they must be valuable and meaningful.
The contest at a minimum must run at least the length of a typical sales cycle.
Never end the contest the last day of the period/month/quarter. This eliminates last minute problems that might pop up due to vacations, illness, etc. And it makes the life of the sales manager easier as all the orders are in and processed on time!
I would like to hear from readers as to what kinds of sales incentives work and what kinds don’t, and the reasons why. If everyone contributes, we can build a treasure trove of ideas we all can share in and increase the success rates of our teams.