The best strategy to gain Gil and high Levels as soon as you get the Canoe Is to fight Warlocks north of Flynn/Phin. If your lucky they'll drop Berserk Scrolls, which you can sell for 5.000 Gill.
Fight them until you have about 60.000 Gill, then take the Canoe across to Ploom/Palm.
From there take the Boat to Poft, and pay Cid to take you to Kashuon.
Go South from there to Chocobos Forest and capture one, ride It down to Mysidia.
There you can buy Knights Armour, Power Staffs, Ogre Axes, Holy Scrolls and Change Scrolls, which are usally only available later In the game.
Equip your Characters with these Items then go to Flynn and start fighting the Soldiers there.
You'll be able to defeat them now within Three turns. They usally drop Gold Armour, Flame Bows, Curse Scrolls and Toad Scrolls which you can sell for 2-5.000 Gill. You can also Level Up alot fighting them.
Do that until you've got enough Gill or are bored, then get on with the game.
You'll be Invincible, so there'll be no challenge, but the game will flow alot faster.