Jenn Tisdale at Brightest Young Things did some wonderful legwork in finding out what comedy festivals are looking for in potential performers.

She asked the folks behind Bridgetown (Portland, OR), Women In Comedy Festival (Boston, MA), Charm City (Baltimore, MD), Comedy Exposition (Chicago, IL), Bentzen Ball (Washington D.C.), Hell Yes Fest (New Orleans, LA & Austin, TX), and Riot LA (Los Angeles, CA) and compiled this nice article of their answers and explanations at the link.