Picking a profession may be a difficult choice for you when starting a character or power leveling a profession. For most people, they have to watch out what profession they choose because of the amount of gold it takes to level it up. That is why most people choose to pick a gathering profession and a complimentary profession to support it. If you are looking to make gold from your profession in the long run, you are best off choosing a gathering profession. However, the downside of having a gathering profession is that you cannot do anything else than gather.
The benefit of choosing a crafting or service profession is that you can benefit yourself. However, the downside is that you may have a hard time leveling the profession as it will cost you a lot of gold as well as time. The good news is that you can still make as much money as a gathering profession in the long run. You just have to simply figure out how to do it and learn the most profitable strategy.
If you are going to gather and earn money through farming herbs, ores, or leather, you should definitely analyze the market and see which items will yield you the most profit. You can then just load up on food and water (if you need it of course), empty all your bags, and you can begin farming in that area for lots of profitable items. If you really wanted to, you can save all your materials and level another profession with them if you have enough guildbank spaces. If you do not buy additional space, you will have a hard time storing all your materials unless you mail them to yourself. However, it will only last you 30 days.
If you are going to take a service or crafting profession, you should definitely first level your profession based on how much gold is available to you. Tailoring will require a lot of cloth, so you should definitely check to see if the cloth are affordable in the AH. The best thing to do is see which class you are and pick a profession that will benefit you. For example, if you are a priest, you should pick tailoring as one of your profession because you can make items for yourself.
Once you have a profession maxed out, it is time to see which things sell the best. Sticking to the tailoring example, you can make 2 ebonweave per session if you are specialized tailor. This means that every 2 days, you can generate and easy 150g profit just by making it really quick. Ebonweave is preferred over the other cloth (in my realm) because it sells better. If your guild has another cloth that sells better, you should definitely specialize and make that.
If you are a blacksmith, find items that people need such as rods. All the rods are needed my enchanters, so there will always be a demand for rods, especially with the ridiculously low competition. These are some of the examples in how to make gold using the items that are in demand.
There is another way to make money off these professions. Usually, the items that you can craft will be a lot higher than the materials needed to make them. You will simply have to go out and see which materials are cheap to obtain and compare it with the item price. The highest yield will be for epic items at level 80. You want to make sure you see the average selling price of the item before crafting them. If the items are items that do not sell very well, there is not really a point in making them as you will end up losing a lot of money.
If you are leveling a service profession like enchanting, you may want to give out free enchants in the process of leveling. If you yell in trade about a free enchant you are offering, you will most likely get tipped for the service. This way, you can get tips and be able to level your profession at the same time which is extremely convenient for you.
As you can see, there are numerous ways to profit from all of the profession. If you can use your profession correctly, you have the potential to make a ton of money through the professions no matter which profession you choose.