You get gold for every time you post or comment, so find a forum or some forums where you feel comfortable, and talk to others.
The game of Booty Grab is a good way to snag some extra gold. While you're posting in the forums, look for aquariums that suddenly are displaying the words BOOTY GRAB.
Log in every day, even if only for a few minutes, and click on the orange machine-thingy on the right side of the Gaia banner. Do this on each page: Home, My Gaia, Shops, Forums, World, and Games. You get gold and items (some of which are salable in the market).
Watch videos for Gaian cash. Click on the cash icon, up where your gold, cash, and achievements stats are displayed at the top of the page.
Buy and sell things. You can buy the Monthly Collectible Letters for 250 cash, and then sell them on the market (or open them and sell what's inside). This will get you started in the market.