Oh man, this FFII journey I'm taking is just getting worse by the day. I'm halfway through the game and finding out that most enfeebling magic is just completely useless.
For example, I'm in a dungeon where there are a few enemies who hit like a truck with physical damage. I just barely got blind magic. Makes sense to use that against them, right?... Well, no. Every spell starts at level 1 and some of them take several dozen casts to level up a single level. In the meantime, the spell has an insanely low chance to even land, so you're either stuck grinding it for hours against low level garbage or trying to level it as you progress, which is basically just a waste of precious MP, a loss of damage, and a lost opportunity to level something else instead, all in the hopes that the spell will eventually be worth the trouble.
Ugh. It really makes me appreciate how good the series became later on, though. Even the job point grind of FFV felt far more fulfilling in comparison.
Yeah, doesn't help that in the old ones, some spells are bugged. Let me lay down some sexy knowledge on you, assuming you haven't gone and found it already.
In FFII there is a king stat. This stat is AGI. Why? It affects your Evade% Evade% actually determines initiative as well as preemptive strike rate, BUT it needs to be high on FIrion specifically to get the 95% preemptive strikes.
It needs to be high on everyone else, or at least on everyone you intend to have in the front row, because almost all late game enemies have En- enfeeblements on their physical hits, including instant death, which magical resistances won't really protect you from.
To raise evade you either need to equip a shield or a weapon that imparts evade, such as the Main Gauche or Defender. You then need to be struck in combat BY ENEMIES. Hitting yourself will not raise your evade.
That's all there is to evade, but it's not all there is to the battle system. More relevant to your magical woes, the magical system in FFII is pretty strange. The accuracy rating of spells is affected directly by equipment weight, meaning that equipping anything lowers spell accuracy and effectiveness, yes, even for healing spells(though to a less extent, because the game doesn't check evasion for hits you do to yourself). This means that you want your mages to be naked, which means they can't gain much AGI or Evade, so you'll want to put them in the back row.
Daggers have the least impact on magical performance, so while it runs counter to the rest of the series, you actually want your WHM oriented character to wield Daggers, since most White Mage is non-offensive, the daggers will be their bite.
If you don't want to grind, then you have to know what you want each character to specialize in from the start, do a little grinding for some nice base MP anyway, and then move on into the game. You don't want to grind one stat too high, because it will cause the stat gains to be harder to attain outside of that one stat.
You will want your physical fighter to be Firion, and Guy is probably the best choice for WHM, due to WHM needing weapons. This is sort of counter to some guides, because Firion is bugged to gain Spirit up from being hit with enemy magic. If you make Firion a mage though, his AGI suffers, and you will be ambushed more often. There are weapons throughout the game that inflict debuffs or target monster families. They all work. The most noteworthy one is the Ancient Sword, found in the Ice Cavern on the way to get the Bell. It has a low accuracy, but it inflicts Curse and most monsters can't resist it. Curse cuts ATP and DEF on monsters by a significant amount, so much so that it lets you do things like kill the Adamantoise with physical attacks. It is useful for the whole game as a debuff.
Spells that are worthwhile to work on:
Cure
Esuna (Esuna 16 can actually heal death)
Shell (mostly for late game)
Life
Berserk(you can actually cause ATP overflow if you level it too high and cast it on a single target)
Aura
Barrier (Late acquisition and actually unnecessary, but still really good)
Fire
Blizzard
Thunder
Flare
Osmose
Curse
Mute
Honestly, the Firion's AGI/Evade being tied to Preemptives is the biggest deal. FFII is usually considered a hard grindathon, because the mechanics for stat gains are so opaque. Most people playthrough walloping themselves to get HP, only to have no evasion, so they get ambushed 95% of the time and then get enfeebled, and then only live because most enfeeblements only last for the battle duration. Also keep in mind you can switch weapons in combat with ones you have in your item hold slot. This helps immensely, because you can debuff say, a Hill Gigas with the Cursed Sword, and then on the next turn switch to your Wing Sword and one shot it.