A lot of you will be leveling professions now into TBC levels. On expansion launches is the one time where you should NOT blindly use profession leveling guides.
Low level profits
THe main reason is that there are usually a lot of recipes that are profitable that do not require max skill. Unless you need max skill to craft a specific BoP, you should generally stop at the first profitable recipe you can craft and then craft that.
Example: Tailoring
One obvious example is tailoring. Cooldown cloth and Bracers of Havok both just require skill 350. Getting to 350 is very cheap compared to 375 and this will save you a ton of gold up front. You will also get paid to level most of the rest of the way by focusing on just crafting these profitable recipes.
Look through the recipe lists
To make the best decisions you should look through the recipe lists for what recipes you are targeting and in range of getting. Then you level up to that point and see if they are profitable. At every stop on the way there you can also check your profession and see if you have any orange, yellow or green recipes that are profitable. If they are then craft some of those and grab the sales.
Don’t overbuy
You also want to significantly avoid overbuying materials. Don’t buy more than you need or more than you are planning to use. Material prices will vary a lot in the near future, and you want to make sure you are making a profit every time you can.