yay for atu2!
From atu2.com's Fan FAQ:
1) My friend/spouse/sibling/kid/parent is dragging me to a U2 show. How do I not look out of place?
Or, I'm into the band now, but this is my first show! What should I know before I go?
Glad you asked! There's only one absolutely crucial thing to fitting in at any rock show, let's face it: at least look like you're having fun. But beyond that, there are a few things that might actually make it more fun.
a) Sing along with "Pride (In the Name of Love)". The fastest way to prepare for a U2 show is to borrow the resident fanatic's copy of Rattle and Hum and learn at least the ending of "Pride". (The song is originally from The Unforgettable Fire, but the R&H version is live, and that's what you need to hear.) Chances are you know this song already; it's one of the biggies. At the end, just about every fanatic is going to do a call-and-response with the "oh oh-oh oh" chant. Bono will sing the first one, the crowd will sing the second one, and so on. This one's practically guaranteed. Also, if you're feeling really into it, yell "The Edge!" right before the guitar solo. (That's on the R&H version, too.)
b) Learn "40", just in case. Throughout the eighties, U2 ended their shows with the neo-hymn "40", the closing song on the 1983 War album. (The title comes from the psalm it's based on.) It became a crowd tradition to take over the chorus ("How long to sing this song...") at the end, and keep it up after the band has left. U2 stopped closing with "40" around 1990, and started to close with Elvis Presley's "Can't Help Falling in Love". However, once in a while they'll end with "40". (I was lucky enough to catch it in Seattle, at the last North American PopMart.) And the more people are into it, the better it sounds. It's a beautiful song, in any case, and not very long. Try it.
c) General concert rule: Know the songs. Sounds obvious, but nothing can take the fun out of any show like not knowing the songs. For a quick U2 primer, try the Best Of 80-90 plus Achtung Baby and whatever they're touring on at the moment. At the very least, know "Pride (In the Name of Love)", "Where the Streets Have No Name", "One", and "Mysterious Ways". Chances are you know part of them already.
d) OK, it would be nice if I could tell them apart...
Always a problem for newbies. Don't feel bad. Okay, U2 is a four-piece, this can't be hard. We'll start with the center. Lead singer: Bono. (See also: Why the odd names...?.) If you can't pick out the lead singer in any four-piece, you really have a problem.
Bono also plays a little guitar, but not through the whole show. Next, lead guitar: The Edge. (See also: Why the odd names...?.) If you ask a fanatic to see a few pictures or liner notes, you may notice that the Edge has rarely been photographed in the past eighteen years or so without some kind of hat on. So, in a pinch, Edge is the one in the hat. (Edge also sings backup, and does the lead vocals in a few songs.) He usually stands on the left side of the stage (the audience's left). Third, bass guitar: Adam Clayton. Yes, some of them actually use normal names. Adam's the one a) wearing regular, non-sun glasses and/or b) playing with his back to the crowd. (Except in PopMart, where it seemed to be a statement, that's usually to communicate better with the drummer.) Unless U2 plans to really shock the fans with the next tour, Adam never sings. (He talked in one song, "Your Blue Room", but they never play that live.) Adam's usually blond, though rumor has it he's gone back to brown. (When in doubt: blond techno, brown roots-rock.
) Adam always stands on the right side of the stage. (Audience's right.) Last but definitely not least, especially to a certain subdivision of fans, drums: Larry Mullen Jnr. Again, it's usually pretty easy to find the drummer in any given four-piece band. Larry usually doesn't sing either, except in one song, "Numb", which I'm venturing a guess won't be played again any time soon. (However, he is known for lip-syncing to Bono's singing. If you have a good enough seat to catch that, congratulations; you are the envy of thousands of fans.) The drummer is, obviously, in the back. Larry is also usually the most conservatively dressed member of the band, and has had the same haircut since about 1984.
http://www.atu2.com/fanzone/fanfaq/
And yes, I'm too lazy to go through and edit that if there's other random stuff in there. Sorry!
Ellen!
...and I told them they all needed to get tickets!!!! 
