Time for a crash-course in gold-making for new gold-makers. So you just boosted a toon to 90, got a profession you don't know anything about, and want to start making gold with it. How? There are a lot of nuances to profession-based gold-making that rely on server differences, niche markets, etc. but here's a basic guide to getting started with whatever profession you've picked up. This is aimed at new gold-makers. If you already know what you're doing there's likely nothing new here. Just be aware this is not everything to know about any profession, just a general intro to basic gold-making with each. Not everything will work 100% of the time, it's up to you to use your brain. Use this as a jumping off point, not a bible.
Also, WTF I just can't help myself from writing educational stuff, can I? Ergh, I'll never escape it I guess. Oh well. Might as well roll with it.
Alchemy is a decent gold-maker on its own but it really comes into its own when you can pair it with jewelcrafting in order to produce large amounts of gems via transmuting. If you have the Jewelcrafter to pair with it transmute Primal Diamonds and any other gem that's profitable. If doing this you really really really want Transmute specialization to get maximum profit. This is the best way to make gold with Alchemy.
Outside of the pairing with jewelcrafting consider making Potions of Luck and Invisibility Potions (You'll need to get the recipe off the Auction House since it's a world drop). If you're specifically not using a Jewelcrafter consider a specialization for whatever you make most often; if you make a lot of Invisibility Potions and Potions of Luck be a potion master, if you'll be making lots of flasks (not very profitable on most servers) be Elixir-specced.
Hands down, though, strive to level a Jewelcrafter if you want to get the most out of alchemy.
Blacksmithing's bread and butter is Living Steel Belt Buckles. Check your AH for the cost of Living Steel bars and the belt buckle, as long as there's a decent gap in prices just buy Living Steel, turn it into belt buckles (1:1) and put them back on the AH. Try doing this on big raid nights when people are likely to be getting new belts.
Use one Trillium Bar per day to make a Trillium Ingot. (Get this pattern as a drop by killing mobs on the Timeless Isle.) Doing this will teach you a new PvP piece pattern and will save up materials to make 553 Epic belts and pants. Roughly every 3-4 weeks you will be able to craft one of these to sell for a few thousand gold. It's not going to make you rich overnight but will give you a few thousand guaranteed gold each month.
You can also make crafted Malevolent PvP gear, patterns you'll be learning while doing that Ingot cooldown; unfortunately its item level is only 476, putting it slightly below what the new boosted 90s will get and lower than Timeless Isle gear. This has taken a huge toll on the demand for these items, however new PvP-ers still will want teh resilience gear. Consider making a couple pieces to gauge demand on your server. If materials are limited stick to belts, bracers, and boots since these can be used by all Plate classes, compared to other pieces like chest and shoulders that are particular to one class and thus have lower demand.
Believe it or not the best way to make gold with enchanting is by enchanting! Use Trade Skill Master or a similar addon to create a group of MoP-level enchants. Craft a few of any that are listed as profitable and sell them. (If you don't know how to use TSM you should learn right now.)
You can also look at other, pre-MoP enchants, like Mongoose (pattern from Moroes in Karazahn) and Executioner (pattern from a vendor in Netherstorm). Use TSM to do some Disenchant scans to resell materials at a profit. (Particularly look for items that DE into Sha Crystals, they're commonly sold for under Sha Crystal value!)
Don't listen to the nay-sayers, Engineering can make gold! Here's what you're gonna do: Make a few of each type of Tinker's Gears to sell on the AH. The mats are very easy to come by, just some bars, and you can sell them pretty high on most servers, I sell mine for 110g each. Make some Ghost Iron Dragonlings, start with just two or three, restock as they sell.
Depending on what your specialization is and what patterns you have you can make a variety of different pets. Some are trainer-taught, others like the Tranquil Mechanical Yeti or Lifelike Mechanical Toad come from quests or rare patterns. Find out which pets you can make, which ones you're missing, and try to track down the patterns you still need. Craft one or two of each that you can and sell them.
Make your Jard's Peculiar Energy Source (Get this pattern as a drop by killing mobs on the Timeless Isle.) every day. If you have a good source of cheap Living Steel you can make the mounts or pets yourself to sell but I usually just post my Engineering in chat when I have enough Jard's and have buyers bring the Living Steel.
If you're more interested in farming head to Zangarmarsh and do your respective quest for your Zapthrottle Mote Extractor. You can fly around in BC or Wrath areas and gather gas clouds; the demand for these items aren't high but they're also not usually very common on the AH so can frequently be sold for a good amount. You won't get rich but it's a good way to get a bit extra out of Engineering. (This pairs well with Mining because you can gather Fel Iron and Motes of Fire at the same time to maximize those delicious Burning Crusade profits.)
The main gold-maker from Inscription is glyphs. Whether you want to sell glyphs or not be sure to do your researches every day. (Minor Research, Northrend Research, Scroll of Wisdom.) Stop one once you've stopped learning glyphs from it. Even if you don't want to sell glyphs now you may wish to one day and you'll be glad you've finished your researches.
You could dabble in glyphs, crafting what TSM says is profitable. There's nothing wrong here getting started but if you are interested in truly competing in glyphs there's more to talk about than a simple paragraph. I recommend this post for new would-be glyph sellers.
Use your Starlight Inks to craft the epic-level Shoulder Enchants to sell. Some servers do well with the Kite pets but the aren't a hot seller on my own. Don't bother with Darkmoon Faire cards at this point in the expansion, there's no real demand. (ep recommends making decks in the comments. I disagree unless your server is very into challenge modes but, if you have the Scrolls to do so anyways, might as well give it a shot. My server just buys carries in CM so there's very little demand, but your server may be different and it may be worthwhile for you.)
Jewelcrafting is one of the most popular professions among gold-makers. It pairs particularly well with Alchemy and Enchanting but can do very well as a standalone profession as well. The main way jewelcrafters make gold is through what is colloquially referred to as shuffling; the act of buying cheap ore (usually Ghost Iron) and prospecting it down, then turning the materials into different profitable items via cutting gems, making jewelry, possibly disenchanting that jewelry, etc. You can do this at a basic level "by hand" by just buying Ghost Iron at a cheap price for your server, prospecting it, cutting all the blue-quality gems into the most profitable cuts (Do your Facets of Research if you don't already have all the cuts!), turning the green-quality gems into jewelry, selling the green-quality jewelry to a vendor, and putting the blue-quality jewelry on the AH. This may not be the best possible route for profit on your server but it should turn a good amount for most. If you want to get more into shuffling check out Xsinthis' shuffler spreadsheet.
Outside of the shuffle be sure you're cutting Primal Diamond meta cuts; the cut patterns are world drops so you may need to play a bit to get the cuts but they're well worth it. For sure cut Burning, Agile, Revitalizing, Reverberating, and Austere. Consider Eternal, Ember, and the PvP-oriented cuts if there's enough demand on your server or you have lots of leftover mats after covering the first ones listed.
If you're on a character that actually gets Spirits of Harmony pick up the leg patch patterns from Golden Lotus and make a few of each to sell.
You can also make crafted Malevolent PvP gear, patterns you'll learn if you do a Hardened Magnificent Hide cooldown, learned via a drop that's common on Timeless Isle; unfortunately its item level is only 476, putting it slightly below what the new boosted 90s will get and lower than Timeless Isle gear. This has taken a huge toll on the demand for these items, however new PvP-ers still will want the resilience gear. Consider making a couple pieces to gauge demand on your server. If materials are limited stick to belts, bracers, and boots since these can be used by more classes, compared to other pieces like chest and shoulders that are particular to one class and thus have lower demand.
With the Hardened Magnificent Hides you can make a belt or legs piece every few weeks for some extra gold as well.
Do your Firelands dailies in Hyjal until you've learned the bag patterns; make and sell the
gem bags, glyph bags, and mining bags.
Do your Imperial Silk and Celestial Cloth cooldown every day. You have two good choices for Imperial Silk; you can use each piece to make Greater Spellthreads to sell; I do this. Or you can save it up and, with August Celestials at exalted, you can make the largest normal bag to sell. Both are good options, I just find the spellthreads more profitable personally. Check prices on your server.
You can also make crafted Malevolent PvP gear, patterns you'll learnby doing that Celestial Cloth cooldown, learned via a drop that's common on Timeless Isle; unfortunately its item level is only 476, putting it slightly below what the new boosted 90s will get and lower than Timeless Isle gear. This has taken a huge toll on the demand for these items, however new PvP-ers still will want the resilience gear. Consider making a couple pieces to gauge demand on your server. If materials are limited stick to cloaks, belts, bracers, and boots since these can be used by more classes, compared to other pieces like chest and shoulders that are particular to one class and thus have lower demand.
Consider Netherweave Cloth and Embersilk Cloth to make their respective bags; these are very popular bags even now and can be a profitable venture for most tailors.
Note that if you do both cooldowns every day you find yourself in need of a lot of cloth. Try to farm it on the actual tailor since they find more cloth than non-Tailors. I pop a Potion of Luck and farm for the duration to increase my profit and cloth-yield.
This is relatively straight forward. Just fly around and herb. A few tips about it: If you have a Sky Golem you'll be able to herb without dismounting just as druids can. If you get Forager's Gloves from Korda Torros or certain mobs on Timeless Isle you will gather even faster.
You could also look at specific herbs from previous tiers of content; Whiptail is easily farmed and important for leveling Alchemy. Ghost Mushrooms are usually pretty valuable due to their value in leveling alchemy and their role in making Invisibility Potions in challenge modes. Goldthorn, Fadeleaf, and Gromsblood are also major Alchemy chokepoints and thus are relatively valuable and may net you more gold per hour farming than MoP-level herbs.
This is relatively straight forward. Just fly around and mine. A few tips about it: You can find an Ancient Pandaren Mining Pick in Jade Forest which (rarely) procs extra gems when mining. If you get Forager's Gloves from Korda Torros or certain mobs on Timeless Isle you will gather even faster.
You could also look at specific ores from previous tiers of content; Fel Iron, Adamantite, Cobalt, and Obsidium are frequently valuable due to their use in things like leveling professions.
One of my favorite things to do is buy cheap copper and tin bars off the AH and smelt them into Bronze. Bronze is not farmed, it is only smelted using copper and tin. Because of this a lot of people don't think to craft and sell it or even really remember it exists. You likely won't be able to charge a whole lot for it but it's some easy gold pretty regularly.
This is relatively straight forward. Just skin dead things. A few tips about it: You can usually run around Timeless Isle without killing anything at all and just scavenge corpses others leave behind. If you get Forager's Gloves from Korda Torros or certain mobs on Timeless Isle you will gather even faster.
Keep an eye on the AH for lower-level leathers without much representation on the AH. When leveling engineering the other night I was paying 20g per piece for Medium Leather because there wasn't any on the AH. Gold from skinning will largely be about serving these under-served markets.