Making gil in the game is a bit of a complicated answer, since there are a lot of different means to be able to do it. The best thing for now is to just level up to 50 and access the later game content. But crafting and gathering are one of the ways to make money. Doing your dailies and running dungeons are another way, though less fast. Running maps is a good way to make money, but it's a roulette if you get anything good from them. A steady cash flow can come from doing some of the easier to make items in crafting that are used in leves, they go pretty good and if you make HQ they should sell. If you want large volumes of gil, but less regular then you'll need to make out a craft with full materia melding and everything, which is a very expensive thing to do. Got to spend money to make money as they say.

Leveling, do your duty finder roulettes regularly for good exp bonuses. Even at the higher levels it can nearly give you a full level. Also dailies past 40 are good. There are also Stone Vigil and Aurum Vale exp parties. The lower level is normally hunting log, some fates and dungeons. Always do your hunting log though, they are great exp. Also do your challenge logs. They are good exp as well.