Give someone an Enemy HP = 100% > Steal Gambit. That way your character should be able to steal once from every enemy you encounter. Also make sure to only buy the equipment you need, if it's just a boost of 1-4 defense or damage, don't buy it. I usually only get equipment when it raises defense or damage by at least 5 or 6. If you can spare any Gil, buy the Grimoires from the Bazaar. They're expensive, but you get better Loot.

Try to do the White Mousse Hunt. The reward you get is well worth the effort, and it will last you a LONG time.