So much is said about the elevator pitch and that you must have one. In a sense it is nothing more than a greeting, as you do everyday with friends, family and work associates. Keep this in mind as you work to find your pitch. It is impossible to spew out everything about you in 15-30 seconds. Sometimes by mearly listening you'll be able to craft a quick, succinct greeting to catch the other person's attention from whence you can arrange your next meeting. It doesn't always happen but do be cognizant.
Remember that the purpose of your pitch is to gain another chance to sit and get together to talk more where you'll want to learn more about the other person.