If you trust your healers, IB after mountain buster to help them out. If you don't, IB before to top yourself off.
When titan stomps, run behind him so you dont get auto attacked. This makes healing easier on your WHM.
Circle pattern bombs are the only ones you should ever get hit by. If you are going to get hit, just pop your cooldowns and get hit. Berserk and Infuriate are defensive cooldowns.
When titan does the square pattern bombs, dont worry about moving to dodge the explosions until he starts his line attack. Having him farther from the "safe side" makes it easier to everyone else to dodge.
Other than that, it is on your healers to play well. A damage shield does wonders. Asking people nicely to virus, and rain of death could help.

I've 4 manned the fight post heart. Working on 3 manning it. Warrior is a perfectly viable tank for titan and the preferred tank for selling titan runs due to its potential to 3 man the fight while a PLD cannot.