The biggest flaw I see with people doing PvP is that players treat it like PvE, assuming the opponents are dumb AI scripts. It doesn't matter HOW well geared you are. If you go up against a rank 100 PvP player in level 1 gear, you better run because chances are he's luring you into a trap.

That leads to the second biggest flaw I see people make in PvP, trying to win it by themselves. If you can get more than half of your team to coordinate on a strategy for winning, your chances of success are pretty damn good (if they regularly play PvP, even better). Teamwork is how you win. Strategy let's you win fast.

You can't assume that your role is going to be the same as PvE. BLM's have a few good crowd control spells, which sometimes play more important part than simply nuking everything. Don't forget to explore how versatile a THM can be with the added cross class skills....