These tips are for random 4's and do not apply to team-based PvP.
Tip #1: Unless you've a Mesmer with very high fast casting, bring Res Signet rather than any other res.
Tip #2: Always bring Res Signet.
Tip #3: Bring along at least one defensive skill. If possible, also bring along a self-heal. You can't rely on Monks in the radom arena.
Tip #4: If you're a Wa/Mo, Paladin build, you can put Mending on someone other than you. You're generally the last one targetted. Put this on a squishy.
Tip #5: Conditions tend to get more mileage than high damage attacks in random 4's. For example, Immolate tends to do more damage than Meteor Shower.
Tip #6: If you bring a pet, spend a few slots of your skill bar so the pet can do something.
Tip #7: Let your group know what your build does at the begining of the arena. A simple "I'm a protector" or "I'm a nuker" will go a long way. If you're playing a complex or strange build, use more than three words to describe yourself.

Tip #8: Simple strategies -- Turtle Up, Follow My Target Call, etc. -- work far, far better than randomly attacking whoever happens to be in front of you.
Tip #9: If you happen to be randomly placed with a Monk who is not a smiter, defend this person (smiters can generally take care of themselves). They'll appreciate it, and your team will have an increased chance of winning.
Tip #10: If you're playing a Monk, remember you have the Smiting line. There's a lot of good, defenisve skills there.
Tip #11: Sometimes adding in a line of skills you rarely use in PvE will just be a remarkable and stunning success. Use this weekend to experiment with little-used skill lines.
Tip #12: Most importantly, have fun! If you're defeated, and eventually it'll happen, congratulate the victors. When you win, and eventually it'll happen, thank the other team for a good game.
I now turn this over to the rest of you to post your own tips and strategies for enjoying the weekend.
cmb