Fairly New, Some Questions~

[Archona]

1. Sell item drops like Scalekin Blood, Hides (Toadskin, Boar, Raptor Skin, etc), Diremite Web, Fleece, and any non-bound item rewards that you receive and don't need.
2. Start leveling a gathering class. Sell shards, crystals, carbonized matter for materia melds, dye pigments, and various other things you gather. Botany will give you things like lumber, various Culinarian and Alchemy materials, etc. Mining will give you ores, gemstones, and other crafting components (Alumen for Leatherworking, Effervescent Water for Natron and Twinthread, various salts for culinary and alchemical uses, etc).
3. When you hit a place where you "stall" leveling (i.e. you run out of quests while needing 1 more level to get to the next leg of quests), use your leve allowances. If any sort of armor or weaponry is offered as a reward, sell it on the marketboards - you'd be surprised at the money you can make off of some of the gear that is rewarded in leves.
4. Not really "making" gil, but avoid teleporting when at all possible. This will eat up your money like no one's business!
5. Start leveling a craft - using the gatherer class you are already leveling to compliment your chosen craft (i.e. Botany for Weaving, Culinarian, and Carpentry, Mining for Goldsmith, Armorsmith, Blacksmith, etc). While most (if not all) crafting classes will require items from all three gathering classes (including Fishing, sometimes!), having even one gathering class available to farm the ingredients you need will cut down on the money you have to spend to level the crafting class. Sell the items you create if at all possible. You can also use the items (if they're something like gear for your battle class) for leveling and take the Allagan pieces instead of gear rewards (which will net you more money).
6. Crush items that you no longer need into materia if they are 100% Spiritbonded. While you won't get a lot of gil for those lowbie materia, it's usually more than you would get for simply selling the item to a vendor to clear out your inventory space.

Just some opinions on these points:
1. I would vendor these, generally not worth trying to sell most of these crafting materials on the marketboard because they sell at 10-50 gil each only.
2. Sure, spare time, leveling a gathering profession can make you decent gil and set you up for treasure hunting in the future. Good idea, but focus on getting a battle class to 50 first or at the very least simultaneously.
3. If you're doing ALL the main scenario quests and side quests, then you shouldn't run out of quests until about Lv44-45. Any EXP dead zones can be filled with leves, or also dungeons and FATEs. Duty Roulette also helps a ton with those dead zones, but you shouldn't run into many EXP problems until the mid 40s.
4. Yup, rotate your 3 favorites and your home point constantly to save yourself gil.
5. Would not bother with crafting at all whatsoever. I've already said why: the gear you can craft is obsolete from quests/dungeon loot, you can buy them cheaply from vendors or on marketboard and leveling crafting professions takes time that you could spend on leveling. Professions will take weeks if not months of work to generate a profit.
6. The materia is typically as worthless as the gear until you get to III/IV materia, but yeah, no harm in disassembling them once the spiritbond is complete. Just don't count on those materia to sell very easily.

You should take gear rewards from quests only when you feel like you need to. Its wise to balance between gear rewards and gil.