check out the dancesafe start-a-chapter guide. it covers basic information on how to get started doing harm reduction work right away. (as well as how you can become an official dancesafe chapter if that's what you're interested in.)http://www.dancesafe.org/documents/startachapter/index.php
limits on what services can be offered vary widely depending local community norms. not all chapters offer pill testing, for example, and whether you do depends mostly on how the promoters and venue owners of the events you work at feel about it. some chapters have offered water but most promoters don't allow it because they make money off of selling water. most promoters are receptive to handing out literature; the few who don't usually don't want a harm reduction group working their events at all.