What nation did you start in?

If you're in Windurst, do what is mentioned above my comment.

If you started in Bastok, I recommend taking all of your starting jobs and leveling them to 10 in Zeruhn Mines. You'll make a pretty solid chunk of change doing this. Bat Wings sell for 1k a stack and they sell pretty quickly. You'll also end up with Zinc Ore and the occasional Iron Ore as well, which also sell quickly. You can even take all of your jobs to 14 if you want to run all of them through Dangruf Wadi, where you can get Hermit Rings and Wild Onions. Vendor the Wild Onions and sell the rings on auction. Same with any goblin armor you end up with. I started with Monk since it was the quickest and easiest one to get to 10, then used my Hand-to-Hand skill on Thief and Warrior. From that point I did Red Mage and White Mage.

I don't really have any tips for San d'Oria, I've never leveled a character there. Maybe someone can help shed some light.

There are also a lot of things that you can buy on Auction that sell higher to a vendor. A classic example of this is low level Scale Armor pieces. You can often buy them for 200g on auction and vendor them from 270~. Helmet Mole, Vegetable Seeds, Grain Seeds, etc are also ones that I used quite often when I first started. Seeds are useless on Nasomi as currently gardening doesn't work, so people will list them on auction for virtually nothing when they could have sold them to vendors instead and gotten MORE.

Lots of repeatable quests and wise use of the AH and junk selling to vendors. I usually start out in Windy so I'm used to hunting the hares to turn in the lost mail pieces and stacking silk and crawler calcs. Both of those can be turned in in sets of 3 to the same repeatable quest NPC but the silk goes for more on the AH. AHing stacks of crystals early on is also normal as most people wait until later on with established Gil flow to start crafting(and leveling new classes lets you revisit the crystal intake again and again). By level 11, I'd had several thousand Gil as there really isn't much for some classes to buy(war doesn't need much in armor or weapons until then, but mages need to spend to buy the spell scrolls).

Once you get to the point you can kill spiders in korroloka tunnel that's the light at the end of the tunnel. Those are 25/30k a stack and sell reasonably quick.