The rules for the contest can be found on the submissions form, but here's the TL;DR version.
1. The footage used must be primarily animated, regardless of the style or country of origin. Some live action content is fine, but the video must be mostly animated.
2. Content must be "PG-13". We try to be as lenient as we can, but anything that's likely to raise complaints from a general convention audience is a no-go.
3. No obvious signs of piracy, such as watermarks, subtitles, or exceedingly poor video quality.
4. You can submit any single video to a maxmium of two AMV League Qualifiers. If you choose to submit to San Japan XII, you can also submit that video to Tsubasacon's contest, or any of our other contests that're currently accepting entries.
Aaand that's basically it. Got any questions? Post here, I'd love to help you out!