I have 4 pets - explorer, herbalist, doctor, animal husbandry.
Explore as often as you can. Grow seeds. Make medicine (or potions if you have an alchemist). Currently selling everything else.
Make sure you check the buy back price against what items are selling for in the stalls. Some items I can sell back for 10FC each and they are in stalls for 8FC - it's not a big difference usually, but it adds up when you're selling A LOT of items.
I'm trying out domesticating animals with my animal husbandry pet and see where that takes me. ^^ All of that up there is making me enough to keep me playing the game. I don't know yet if there are better/faster ways to make money. Will be watching to see what everyone else says.