Here's a bit of advice when considering what weapons to use: Don't let the attack power of guns put you off them. I recently started again (I'm at the Mosphoran Highwaste) and yesterday my Balthier was equipped with a gun that had like 14 attack power, before swapping it for a bowgun that had like 41/42 or something. With that bowgun he was doing 400-500 damage. But today I bought a gun that had significantly less attack power (around 24 I think), however it was doing damage between 900 and 1100, depending on the monster. Y'see guns ignore an enemy's defence stat. Just as poles do damage based on an enemy's magic defence rather than physical defence.

Another thing is party structures. I recommend having a tank - someone who has high HP/defence, the lure status (inflicted by "Decoy" magic), to make sure all attcks are directed towards them, and then the protect status for extra defence. This would usually be best as the party leader. Then a second character to be a damage dealer - the only gambits this character should have are attacks and get others to cast haste and berserk on them. Finally you should have a spellcaster to handle healing. It's ideal for this character to have a long range weapon or one that increases magic power. Usually I have my tank cast support magic and some back-up healing too.

One last thing I'll add is that you should concentrate a lot on the augments section on the lisence board (directly under the magic section), because it has HP, strength and MP cost upgrades among other useful upgrades, and is neatly right beside the white magic too. To speed this process up you should purchase 6 Gold Amulets from one of the merchants as soon as you reach Mt. Bur-Omisace and keep them equipped all the time (they double your lisence points earned after battle).

That should be the basic everything lol.