How to make a lot of gil

There's a gil farming guide at gamefaqs, but it deals with near endgame, endgame, and postgame farming. In the beginning of the game there's not really much you can do to farm gil other than selling components. Most components sell for a pittance relative to the cost of anything you might actually want to buy, so it's generally more worth it to use them to upgrade your accessories (heavily upgraded +str or +magic accessories can really make the early game easy.) There's also not much to buy anyway. PSICOM or Guardian Corps enemies have a chance to drop a Credit Chip, which sells for 500 gil, and has no other purpose. There's a few encounters in the early game that I think always drop them since they're sort of like minibosses. You won't see very many enemies that drop them until around chapter or 8 or 9, when you get to Palumpolum.

Here's where you can start farming in earnest. Spoilers follow. Each area is better farming than the last.

When sneaking in to Palumpolum there's several groups of PSICOM/Guardian Corps dudes patrolling that you can farm semi-effectively. You can go from the save point, to the end of the tunnel, then come back. Only the earliest ones will have respawned, but you can save and reload to respawn them all.

A little bit later after after Snow meets back up with them, is an area where's there's more larger groups of soldiers. These also are the first enemies who can drop Incentive Chips which sell for for 2500 and like the Credit Chips are meant to be sold. There's usually one or two in each group who can drop it and have Credit Chips as their common drop. Once you get the rhythm of 5 starring the fights (I found Rav/Rav and Rav/Com paradigms, with Med/Sen or Med/Com only when you're really hurting to be the only feasible way) you'll normally get maybe 3-4 credit chips and an incentive chip or two per run. There's also a couple enemies that can drop Rhodocrosite which is used as a catalyst. It takes about 5-10 minutes per run, and there's a save point on either end of the area so you can just save and reload.

The next area is at Hope's dad's apartment, where there's two groups of PSICOM guys that endlessly respawn if you walk a short distance away. The apartment is roughly circular so you can just run down the hallway in one direction until you get tired of farming them. There's more incentive chip droppers in these groups. It's also about when there's some nice accessories you may want to buy (I think 2nd tier str and magic stuff) and upgrade. This place is pretty awesome since it's essentially infinite enemy density. About 5 seconds between fights.

The last is around the middle of Chapter 10 (I think) where you're on the big airship, and there's a big section of hallway with about 7 groups of 3-5 PSICOM guys that drop both Credit Chips and Incentive Chips. There's a savepoint as well as a door to another section of deck you can go through to force respawns. Basically same song and dance as the previous parts.

After that the next (also much more effective) is the chocobo farming which is in linked guide.