Ok, maybe this's just me, but i've been through alotta ballistas.
Many ppl likes to duel, or solo someone. I used to like that too, run into other's camp and start spaming my strongest atks. After a few ballistas that i've done with the jps, i notice that doing ballista is not really just beating each other up; instead i feel alot better when i save a teammate than rape up a mage or something. I've seen most "good" players in ballista never work alone; they alwasy stick with a group.
A rdm for example. One time i had a rdm in my team, I notice that she was getting damage like crazy, it was then i notice that she doesnt have any phalanx or stoneskin on. Instead of getting her self well protected, she kept us all alive, so we can go back and help her. I don't mean that those rdm that uses phalanx and stoneskin are wrong, just that they like to work alone, but even if no one can hurt u, they might go after ur teammates who r weak, such as other mages.
That's just for if u really CARE that ur team wins, if not, then go and kill as many as u can.
I think the key thing to really win the match is to work together, which im sure many of us knew already. For those jobs that r independent, is better NOT run off and kill as many as u want, instead, stick with the jobs that r not that independent, and help them when they're being chased, and they can help to keep u alive too.