I would definately, absolutely, positively recommend this to anyone starting a new game:

Explore.

I think alot of people didn't see it when the game came out - exploration is what most of the fun in the game is all about. Try to make out the entire map for yourself - if you get the map, check out all the areas you haven't yet. Hug the edges then move into the center. FFXII is a game with alot of attention put to environments, so seeing everything and taking part in the world is one of the parts the developers intended the gamer to get out of it.

If you do this, you'll most likely find a few good pieces of equipment out of random treasure chests, not to mention rare drops from some of the enemies. Also, if you take the time to explore every area before moving on, you'll more than likely have all the exp you need, and the gil to get the equipment you need. It's worth it for alot of reasons.

So by exploring, completing mark hunts, and playing through the storyline you more than likely won't have to powerlevel at all, you can just play right through and enjoy.