I've both judged and I've entered at Megacon, so here's a few pointers!
Pre-register on Anime Sushi's website. This way you know in advance your number and can arrange a time slot that is convenient for you on Saturday.
Bring references, and bring progress, but make sure not to bring TOO much. Try to keep it consolidated for the judges.
Make sure that the source is from Japan, please. Anime Sushi is very strict about this.