Final Fantasy Tactics Walkthrough

Depending on how you respond to the situation at the beginning of the battle (A man, Argath, obviously in trouble), the battle objective will change.  If you say that your mission is to destroy the Corpse Brigade, then the objective will be to defeat all enemies.  If you say that you must help the man, then the objective is to save Argath.

Choosing the former will allow you to attempt to farm treasure or crystals again, as it will remove the requirement to keep Argath alive. Either way, the battle isn't too difficult.  The main thing to remember if you've elected to save Argath is to try to get a Chemist within item-throwing range pretty quickly so he can be healed up. This means you will likely need to put the Chemist on the front line of your formation and on the left side of your screen, or stage right if you prefer that way of thinking about it. The Chemist's job can be made easier if Ramza had enough JP to learn Tailwind, because that can improve the Chemist's relatively low speed.

Though Argath and Delita don't have very good AI, they still hit harder than your characters, who are still basic Squires, so it's definitely important to keep them healed up.  If you have an opportunity to choose which enemy to take out first, choose the Thief, but they generally hide behind rocks so it can be difficult to choose.

Advance your troops cautiously - the best way to win this battle is to get two people on two different sides of an enemy and to pound away.  Heal when necessary - buying extra Potions before this battle really helps.

After the battle, the man will introduce himself as Argath and inform Ramza and Delita that the Marquis has been kidnapped.  Argath requests to go with you to see Dycedarg at Eagrose so he can request help for the Marquis.

Heading there will advance the story and then will send you back from whence you came; this is the first time you'll have a little freedom to shop and also fight random battles, as long as you stay between Eagrose and Mandalia Plain.

Consider restocking on items and upgrading equipment, and possibly traveling back and forth to trigger random battles back at Mandalia Plain to level up and unlock jobs a bit, as the first truly tricky battle of the game is on the horizon. Grabbing two Bowguns is a good idea, if you're going to train enough to unlock Archers, as this is your first opportunity to get on-level ranged weapons from a shop.