Usually at that point of the storyline stick with Fang/Lightning + Vanille/Hope + Sazh
You pretty much need Sazh for his haste, enfires and enthunders, Hope has Haste but he gets it pretty late in the game.
Roles (In order as above) Com/Sab/Syn (Vanille only) Rav/Rav/Rav (Lightning only) Med/Med/Sab (Lightning only) Com/Rav/Rav Com/Med/Syn Sab/Sab/Syn (Fang only)
Imperil+En(element)+Deshell works wonders in this team, you'll break everything you encounter in no time, then switch to Com/Rav/Rav
What you do is start off with Com/Sab/Syn (Vanille) or Com/Syn/Syn (Hope) and wait for buffs, if the going gets bad, Com/Med/Syn buys time for the rest of the buffs. Sab/Sab/Syn is an extremely offensive Fang-only combination, Fang provides Slow, which means if your party is hasted you take 4 actions while the enemy would take 1. For Lightning however, you can have an additional Med/Med/Sab(or anything you fancy) for Light's Curas.