When it comes to making money while leveling your WoW character, most of the people will advise to take up two gathering professions until you're way into your 40 and I would even advise to keep it into your 60's. I am actually leveling my Draeni Shaman in this manner, and boy do I have tons and tons of gold :D.  But is this a good advice, and is it the best in all cases?

If you chose to start leveling a crafting profession without having another toon to provide you with extra cash you will be a very very poor WoW soul. This I've learned the hard way when I just began my WoW journey. It is possible to enjoy the items you craft while you level, but you will be very tight on money.