For each contest, the first few GOOD answers I get will automatically go up. After that, any submissions that are better than the bottom one will be inserted into the ranks and bump everything below it down.
There have been several people who submitted multiple times to the same contest. This is perfectly OK! You can submit as many as you want. (Note that if I get 20 messages for the same contest I am likely to become bored with one person's repeated trys, but there shouldn't be much of a problem.)
The current contests are: