Most efficient Chapter One JP farming?

Here are some suggestion I remember for playing it on the PS1 and PSP (I doubt that there have been any drastic changes in the iOS version):

If you get all your characters to have the Squire's JP Up and the Focus skill, there's a simple trick you can do:

Get into a battle with some group with a chocobo. Taking out other enemies EXCEPT for the Chocobo.

Keep attacking the Chocobo until it's low on health (it'll look like it's crouching or knelling) and then try to corner, surround it your characters, and wait for it to use it's Cure to heal itself. Then have one character attack the Chocobo with a weak attack (enough to get it to low health, but not enough to one-shot it when its low on HP). Have the other characters all use Focus and then wait. You can continue doing forever if you want to.

Alternatively, you can use Black Mage with the Toad spell and cast it on everyone, but make sure you first kill anything immune to Toad. Then turn on the AI and let it do all the work. You'll most likely be left with a nice handful of levels and JP when you're done with the battle.

To summarize and add to what Krazer has stated:

General Farming in FFT:

It's pretty much always the same no matter how you do it. Use reduced damage attacks and heal. Rinse and Repeat.

Skills: (that are beneficial to farming)

• Frog. Reduces units attack to 1 (usually if they have a high enough Physical attack is my be a bit more).
• Potions. If cash isn't an issue then swing-away. Just get a chemist and throw them potions.
• Breaks/Ruins. Speed Break will reduce the number of turns the enemy gets so they can't attack you as often. Power & Mind Break will reduce the units Physical and Magic damage to a really low amount allowing for simplistic farming.
• Steal Experience. This along with any Steal skill is a no brainer. A word of caution with Steal Experience though. Don't use it too much or you'll find yourself vsing lv 20s when most of your party is lv5. I made this mistake once. It resulted in 5+ hours wasted haha.
• Gained JP Up. I'm not even going to bother explaining this one, it should be obvious.
• Auto-Potion. For those of us who can't resist the JP-Glitch you probably have this from the start. Disable it. It's a potion that is used but doesn't yield experience. If farming is your goal, disable it and heal as an action.
• Steroids. All skills that buff you permanently. i.e. Accumulate, Yell, Scream. Sadly the Squire ones are the only ones I can think of, but I don't seem to recall any non-squire ones so this might be it.
• Calculators. (I know they're not really Chapter 1 available but I figured it would be worth mentioning) Their spells cost no MP. Spam them everywhere.
• Chakra. The monk skill chakra heals HP & MP. This is a great way to avoid the cost of potions if you put them in combination with a priest or just use Chakra only to heal.
• Equip Change. Free skill, trap an enemy, and unequip your weapon for low damage and the same amount of Exp/JP. Finally a use for this :P

As you can see nearly any skill can be used as a farm-tool, you just have to know what is available and accommodate.