Like others have said, in terms of gameplay, gambits and licenses are probably the most prominent features in FFXII.

Licenses: From the get-go, it'd probably be in your best interest to try and gain all of the licenses you can afford and need. FFXII isn't a game where you can glide through without lots of leveling and combat. Slaying monsters will not only be fun, but beneficial, as you gain EXP and LP. Focus mainly on gaining LP, EXP will gain along with it, and try a get a good chunk early on.

You'll also probably need to do a bit of leveling up between heading for your next destination. For example, if you're in Place A, and you need to get to Place B, you oughta level a bit before heading there. It's always better to be a little too prepared than not prepared at all! xDDD

But don't worry, as you progress and kill more monsters with higher LP, you shouldn't have too much trouble if you spend wisely. And by the end of the game, if you've done most of the sidequests and a lot of exploration, all of the characters will have all of the Licenses anyway.

But until then, Gambits will be important. Very important. Their importance will fade gradually as you get farther and farther into FFXII, but early on, you'll need to pick and choose carefully. Each character should have their own area of expertise, and given a "job". For me, the best way was to divide the entire party was in 3 pairs, and each pair was given a sort of job. What I did:

PHYSICAL
  • A Physical character specializes in (obviously) physical combat.

  • The Physicals will wield close-range weapons, such as Axes, Hammers, Swords, Spears and the like.

  • My Physical characters wore Heavy Armor, and usually had a shield on hand.
  • The Physicals spend most of their combat time engaged in hand-to-hand stuff. Axe swings and sword blows, and all that jazz. They are counted on to do physical damage. Don't normally deal in magic, but may frequently use White/Green Magick
  • My Physicals were (mainly): Basch and Ashe


MAGICAL
  • Magical characters will specialize in Magicks and long-range combat.
  • The Magicals will wield long-range weapons, such as bows, guns, or crossbows, but also be proficient in Staves, Rods and maybe Poles.
  • My Magical characters wore Mystic Armor, and usually magic-oriented accessories.

  • Deals heavily in Magicks, and should be able to use their skill according to the situation. For example, while fighting a foe, a spell from the Black, Arcane, or Time magick family may suffice. But if an ally is in need of help, White and Green magicks can be your best bet!

  • Magicals should be kept at a distance from physical enemies, and constant movement stimulates MP regeneration.

  • My Magicals were (mainly): Fran and Balthier


WILDCARD
  • Wildcard characters are sort of a combination of Physical and Magical. They don't explicitly specialize in either category.

  • My Wildcards wore mainly Light Armor, and pretty much any accessory I felt like giving them. When wielding a one-handed weapon, a shield was present.

  • Wildcard characters can wield virtually whatever weapon you'd like. However, they're usually best with a weapon that suits their individual style. If they have a Physical inclination, give 'em a Dagger, for a Magical inclination, give 'em a Staff. They have plenty of wiggle room in that aspect

  • The Wildcard is not an expert in either physical or magical combat, but they are able to switch between them easily. If your party is in need of healing, the Wildcard may be called upon to help heal or cast spells alongside the Magical. Likewise, if you have a particularly strong foe and the Physical needs help, their aid should be readily available. Usually they're just attacking physically.

  • My Wildcards were (mainly): Vaan and Penelo


Of course, as the game progresses, these basic roles will overlap and a character may end up being a combination of the roles. I know that Vaan was a mix of Wildcard/Physical, and Ashe was Physical/Magical...It's not as complicated as it sounds. And I always made sure that I had one of each in the party. 1 Physical, I Magical, and 1 Wildcard. Easier that way. Though, later on in the game, such roles may seem arbitrary (by the end, all of the characters are virtually the same), but it's still fun to use them! xD

But of course, you don't have to follow any of what I just said, but i'm just telling ya how I did it, and worked for me.

PS- Whoa, such a long post! I'm so tired! Past 3 AM, I need some sleep! ;_;