E-mail address and cell/work phone numbers.

Agree with most thats already said.. especially about not getting fully honest answers to rehearsal conflicts..  Three things that I do on my forms that, while they may not fix any of the problems, let people know that I take it serious, even if they may not.  If I have kids in a show I always ask what kind of grades they are getting.  If a kid is on the border, I like to know.. If there is a possiblity that rehearsals are going to further drag their grade down, its a red flag. I have had "non theater" parents yank a kid for grades, usually at a crucial moment in production.  Second, for all my shows, I have a small paragraph at the bottom outlining the resposibiilty of taking a part, learning lines and blocking, taking care of materials, scripts, costumes props etc... participating in associated activities as much as possible to help build the team, set builds, painting, parties etc. and a reminder that being 10 mins late in a cast of 9 makes for an hour and a half of waisted man hours. and that such behaviour is disrespectful to fellow cast members. 

The disclaimer MartyW mentioned about responsibility is a big help.  Point it out in your opening remarks, too.  Also, this blurb can include (and you can reiterate verbally) that "having a conflict will not preclude you from being cast, so please be honest and list all your conflicts so I can schedule around them."  I have found that to be helpful.

Listing the actual schedule helps, too. 

If it's going to be a big turnout at auditions, I number the forms beforehand, and have my stage manager standing by with a camera and numbered index cards, to snap a quick headshot (with the number in frame) so we can put a face with every sheet.