How to most effectively level your crafting professions

I recently had the experience of power-leveling jewelcrafting twice; once with my shaman, and once with my death knight. It taught me a few lessons about power-leveling that I think can be applied to any profession you wish to power-level. Please note that the tips I provide here are based on the assumption that you are farming the materials yourself. If you wish to power-level your profession by buying stuff from the AH, then use these power-leveling guides. They are also really good for leveling your gathering professions, although you will sometimes need to do your own research on wowhead to see which zones are truly best for leveling your herbalism/mining based on the density of spawn points. Anyways, on to the guide.

The way I went about leveling jewelcrafting is that I looked for an area that was good for farming the general material I needed. For jewelcrafting/blacksmithing/engineering, this means farming copper/tin/iron etc. ore. For leatherworking, this would mean killing beasts to skin. For alchemy/inscription, this would mean farming herbs. Farming herbs for the specific purpose of leveling alchemy gets complicated, but if you are leveling herbalism along with alchemy, just use the herbs you obtain. A good farming area should have spawn points that are really close to each other or create a path you can follow for maximum yield. It's also a good idea to look for an area big enough that you won't need to wait for your mining nodes/beasts/herbs to respawn. An example of an ideal area is Mulgore for mining copper. The route is a simple circle, and the zone is big enough that you shouldn't have a problem with respawns.

Just a few extra notes. Mining nodes will only appear on rocky slopes. This usually means the edges of zones and any mountains, and also means you won't find many in flat zones. Some herbs will only appear on a flat area, while others only appear next to trees, and some only appear on rocky slopes. Respectively, those herbs tend to look like flowers, leaves, or roots.

Once I had a plethora of materials, I went back to my profession trainer and used my materials to make stuff next to them. Every time I increased my skill by five, I checked to see if a new recipe was available for training. The key to this method is how you use the materials at your disposal to level your profession of choice. It's good to create a priority list for which recipes and which materials you will use first. The idea is to use your materials as efficiently as possible while using as many as possible. Materials become less useful as you level a profession, so you will want to use your materials in such a way that none go to waste. For example, in leatherworking, there is a recipe that allows you to turn ruined leather scraps into light leather. There is also a recipe that allows you to turn light leather in light armor kits. Both are very efficient ways of leveling leatherworking when you are at a skill level of one. Also, the first recipe is the only one that uses leather scraps. So, suppose you have a bunch of light leather and a bunch of ruined leather scraps. If you use the scraps first, you can still use your light leather for more advanced recipies later on, allowing you to get some skill ups out of both materials. If you make the armor kits first, however, and skill up that way, you will have lost the opportunity to use the scraps for skill-ups. Thus you will not have leveled as efficiently as you could have.

As should be clear now, efficiency is not only about using as few materials as possible in each recipe, but it is also about getting as many skill-ups as you can out of your pool of materials. Thus it is important to make a priority order of which materials you will use when. Some professions may not allow for that kind of flexibility, but just do what you can. Here's my priority order for power-leveling professions.

1. Recipes that use materials that don't have any other use
These include the recipe I mentioned above by which scraps can be turned into light leather. I also encountered a similar situation while leveling jewelcrafting. While farming ore for jewelcrafting, I got a lot of stones that had no use other than making statues. Thus I used the stones first and crafted as many statues and I could before moving on the using the ore. That way I used less ore to level jewelcrafting than I would have if I used the ore first, and the stones did not go to waste.

2. Recipes that make items you will use in later recipes
The professions are full of these. Alchemy has you making oils out of fish, blacksmithing has you making grinding stones that are used in other recipes, engineering has a plethora of such parts, as does jewelcrafting, and leatherworking allows you to combine pieces of leather to crate the next teir of leather. Be careful that you don't make too many of these parts, however. Some recipes require both the parts you make and the materials you make them from, such as the engineering recipe for a rough copper bomb. This recipe requires both a copper bar and a handful of copper bolts, which are made from copper bars. Thus, if you used all of your copper to make bolts, you'll be out of luck. A good guideline is to try not to have more of the crafted material than the original material. If you have, say, 40 copper bars, you wouldn't want to make more than 20 bolts. This would leave you with 20 of each. If you use them all and end up needing more bolts while needing the bars less than you thought you would, you'll be able to make more. If you end up not needing that many bolts, you'll still have gotten the skill-ups with wasting too many of the bars. You should also just look ahead to see whether or not you will use a certain part. Still, making parts is often the most efficient way to level a profession, so don't worry too much about going overboard.

Once you have gone through these two options, you'll want to use the recipes that use the fewest materials. It's important to also look to see what your trainer will be able to teach you in the future so you can plan which recipes you use. For example, let's say you are leveling jewelcrafting. If you have some shadowgems and some malachite, you'll want to use the recipes that use the malachite first. Why? Because shadowgems are used in higher-level recipes than malachite, so they stay useful for longer. You won't encounter too many situations like this, you should keep an eye out for them.

Aside form that, just use the recipes that use the fewest materials possible. Also, it's worth mentioning that if you are a higher level than you would normally be if you were leveling your profession while leveling in general, recipes that are yellow will almost always give you skill-ups. If you have a skill level of 50 at level 60, yellow recipes will probably give you a skill up. If you have a skill level of 50 at level 10, this probably will not be the case. Thus, don't be afraid to use a recipe that is yellow if it uses less materials than an orange recipe (as it probably will) out of fear of not getting a skill up.