Oh, and be sure to read the rules
There is a waiver for you to sign (if a member of the troupe is younger than 18, a parent/guardian has to sign the waiver for you). The waiver basically says something on the line of "I won't sue Kumoricon or anyone else if I hurt myself while competing".
From previous experience being a judge, be certain your dialogue is understandable -- we can't think your joke is funny if we can't hear it. Practice practice practice.
Although recording isn't required, many groups record their soundtrack prior to the convention and then practice with the recording to ensure that their lip sync works well with the recording.