1. Decide on a theme for the next competition (or find the winner of the last one and ask him to decide)
2. Prepare the guidelines for the theme and start a new thread for it along with the dead line for the contest
3. Watch over the thread all the time to answer any and every question that crops up.
4. While the competition is running try and search for people who would like to donate prizes.
5. Also try and get good mature volunteers for judging the competition (and make sure they aren't taking part

)
6. Find a host where people can upload their levels securely (without anyone able to spy or steal someone else's entry)
7. Remind people of the deadline a week or so in advance.
8. After the deadline, don't accept any more entries.
9. Send the links for the entries to the judges along with prepared guidelines for scoring. Make sure the guidelines cover all the aspects fairly.
10. Try and get the judges to send their scores as soon as possible (without hurrying them too much)
11. Total up the points for each entry and sort out the order.
12. Update the thread with the winners.
13. Make a new thread with the links to all the participating entries and the winner list.
14. Try and help the winners get in touch with the prize donators.
15. Ask the winner to decide on the next theme. Also, whether he wants to be judge next time or participate.
Keith, Fred...did I miss anything?
Now I know why you don't want to do all this every month
-- game dev is fun...but taking up too much time --