Gil will get you a lot of things in Final Fantasy XI. Eventually, down your career in FFXI, you will need to spend your hard earned gil on some really expensive items. For example, as a Samurai, I had to purchase things up towards a good 5 million or so gil. Something as high as that can be discouraging but there are ways to get around this and "farming" (the act of going out in the field and killing monsters for gil or a sellable product) isn't just the only way.
Lets start at lower levels and habits to develop. At lower levels, your demand for gil isn't so high. You need a million gil off the bat but you will need quite a bit to get your spells and early gear going. It would be pretty difficult for even a new player to start getting their fancy gear going and trying to maintain that gil for later on is going to be rough. So, what can you do? At lower levels, there isn't too much of an option from 1-10. However, think about it as this: "How much gear do you really need to hit level 10?" Not many and in all reality, you can hit level 10 with just your RSE gear and maybe at least upgrade your weapon. So, if you don't really need to, don't bother spending the extra gil for items that you don't really need...
HOWEVER ... Once you hit a party environment, it would be very unwise to stay in your weakest gear as there might be other things that can benefit you greatly and allow you to kill more efficiently. After all, if you think you can hit 75 with just your RSE level 1 gear, that kinda negates the point I'm making here. So, lets try to be frugal here but not gimp yourself where you'll be a walking paper bag that can't do anything. First off, lets actually try making some gil here...
You would be surprised what you can make some good pocket change with at a lower level. When you get to a higher enough level to walk around Giddeus/Ghelsba Outpost/Gusgen Mines, try bringing out some Sickles, Hatchets, or Pickaxes and do some harvesting, logging, and mining. Some of those things end up being cheap and should be NPCed or even tossed at times but quite a few things can net quite a bit of gil. It can be a long and tedious moment but also try to keep yourself occupied. Make it a game, like it's supposed to be. Just try to think about how fast you can hit each point and move on to the next one so you can constantly pull the resources out of them.
If you want to spend a little time and set yourself up a bit for the future, fishing might be up your alley as well. If you level up your cooking a bit to around 29 and make yourself Insect Balls, you can fish up a lot of moat carp within your nation's walls. Granted, you would be limited by the fishing limitation they placed (200 some fish I believe the cap is), but if you choose not to do the associated quest with it, that's about 50k a day you can fish up depending on price and the demand for moat carp is pretty high. Fishing in general can even get you some nice money if you're not doing much of anything.
Now, if you want to try your luck, you can go into the Chocobo Circuit and bet gil on the best two chocobos in a race. However, it can end up being very random and difficult to predict. Alternatively, you can raise your chocobo and compete against these chocobos for some gil as well. If one were to win the C1 Race, that's 100k gil per day with a 10k bet. Not too bad if I say so myself.
These are all just a few alternatives you can do to get some gil in your wallet. Of course you can always farm but please make sure you research what you're farming and try to get more gil out of it with every second you spend out there. Time is money so try to make the best of it and don't spend too much time going out there for nothing.
Now as for habits, lets list a few:
1. If there is a significantly close or equal item equipment that you can get at a later level, save your gil and wait for then.
2. If you're a mage, don't even worry about too much about any equipment that has only defense on them. Sure, you can argue that you'll need it to stay alive if a mob hits you... but if you don't make the mob hit you, you would have no problem, right?
3. While food makes your character powerful, try to be light on it if you can. There are food out there that don't cost a ton but will make your character efficient. Likewise, there are food out there that are pretty expensive but they don't suit what you're doing. Would be pointless to use something like a Carbonara if you're not even /SAM or tanking something in a merit party, for example. For the 75 people out there, just don't use food at Bird Camp. I mean it's great for killing things faster and all but if you're the only one using it, you're constantly eating them down. Maybe it works if you have all the people using food and keeping up with the hate but that's money saved regardless.
4. Avoid using Whitegate to sell your items. Go to Jeuno or Tavnazia and save the precious little bits of gil for the transaction fee. If anything, bazaar your item outside of Jeuno if the item is a few hundred grand or million.
5. Use up your Imperial Standing as a mid-high leveler. Sell of your Gold Coins as they are always in demand for certain items in Aht Urhgan.
6. If you have nothing better to do, Besieged or Campaign when you have the chance. Besieged gets you some Imperial Standing and allows you to skill up and kill some stuff. Campaign doesn't really net you a lot of gil with Allied Notes (but it can if you look around a bit) but you gain XP without having to jump into a party and you don't have to worry about consuming food or spending much money to get to where you need to go.
7. After every update, research new items. If you get the jump on things, people usually buy things at ridiculously high prices. Don't feel bad about the people, feel good about the money you're making due to another person's impatience.
8. Overall, just keep a note at what is hot, what is cold and what hidden things you can find that people can take a bit of an advantage of.
Of course, you can forgo all that and buy gil... but, that's up to you. I won't say it is a bad thing or say it is a good thing, I will say that it is against Square Enix and PlayOnline's Terms of Service to involve real money trade with the items in game. So, if you do buy gil, you know the risk.
In a later post: More gil making options and maybe a little light on some Chocobo Racing!
Oh, and I would like to make a quick reference to my personal blog for Campaigning. It is a little guide to figure out how to get the most out of Campaign for jobs that can't really do those battles that well for EXP. However, it can be used if you want to be a little bit lazy but don't try to do it too much, after all, the fate of Vana'diel's past does lie in your hands.
The post can be found here: Campaign Battles and Earning XP