Unlock the Hunt and do the daily and weekly Hunts on the Hunt Board for special hunt currency (Allied Seals for GC Hunts, Centurio Seals for HW and SB Hunts, Bags of Nuts for SHB Hunts), and then trade them in with the Hunt vendor found near the Hunt Board and buy Aetheryte Tickets - these allow you to teleport for free, and given the tickets cost very little in Hunt currency, you can fairly quickly amass a huge stack of them, meaning you will never have to pay gil to teleport anywhere ever again! (You wouldn't think so but teleportation charges do start to drain your gilpouch).

KDSilver already mentioned it but I'll add something further: retainer ventures - if you send your retainers out on 'Quick Adventures', sell everything which is sellable they bring back, no matter how apparently insignificant it can be, as it all adds up. Any 'green' or 'blue' gear they bring back trade in for Company Seals at your GC instead.