The PSX version is underated. While the translation is lackluster, it is much easier to aquire all the skills and rare items. Winning the game is moderately difficult, mastering it is is very challenging.

Some suggestions:

1) Accumulate is the best way to level up generic units, but most nongeneric unit do not have Basic Skills. The best way for them is to equip the Thief's Steal Gil. Hitting a unit from behind, they almost never miss and you increase your lucre at the same time. The other requirement is Gained JP Up. Don't ever bother with Gained Exp Up, since if you master every profession you'll max your levels long before you max you jobs.

2) In random battles the foes stay at commensurate levels to your own party, but in boss fights they stay at fixed levels, so you can always level grind your party to deal with difficult fights. You can almost always muscle your way through a boss fight, although in most cases there are specific strategies for winning.

3) The shops update their stock every time you advance the plot. It's important to keep at least your active party equipped with the best protective gear. Once your best armor is becoming ineffective against random foes, it's time to advance the story.

4) Generally the best job class for nongenerics is their own basic class, although with Mustadio can be an Engineer/Chemist or Chemist/Engineer either way. It's fine to have Agrias use Equip Sword when training in other classes, but once you get access to Knight Swords, you'll want to keep her as a Holy Knight, at least for boss fights.

5) There are many classes that have strength and weaknesses, but I feel the best generic class is Calculator. Or more specifically, Math Skills (the stats on the class itself are terrible). Math Skill allow you to cast almost all the spells of the White Mage, Black Mage, Oracle, and Time Mage instantly with no MP cost. It take time to work out the best claculation that benfits the party and damages the enemy, but once you, it's lethel. Once your party is level 99, you can always calculate against Level and multiple of 3 to hit the party and some other multiple to miss. It's my secondary skill set of choice.

6) Mediators will be absolutely necessary if you want to recruit monsters. And to be heartless, some of the rare items can only be gained by poaching your own monsters. In the end, there are terrific monsters that can deal tremendous damage to foes, although they are not as versitile as human units. My favorite monster are the three-headed Tiamats.