Recently WebYA posted a fabulous list for someone looking to start a teen advisory group (and by recent, I mean it was March 2010 so recent enough). I've done a lot of research on these groups in the past year (Tuccillo's book Library Teen Advisory Groups, YALSA's TAG resources* and then there's always the TAGAD-L listserv) and I have to say I really like this list a lot! It's succinct and yet every detail is important for someone starting a TAG. It even has ideas that I didn't come across in any of those numerous resources. Check it out if you are starting a TAG or even if you've just celebrated the 4th anniversary of your library's group.
*Which could use work, to be honest with you. Some links are dead and many of the "Still in development" sections were in development when I looked at them last summer