WOW power leveling is an interesting beast to tackle. There are many ways to do it, many people trying to sell you their method of doing it, and of course many advantages and disadvantages to all the different ways. As an above poster mentioned definitely join a guild (at least level 10 or something like that for the 10% increqased XP gain) and as its the social aspect of WoW that really makes this game outstanding. If you have access to heirlooms or recruit a friend (RAF) this process is much smoother and quicker. Also for the love of God when you get the chance buy the biggest bags you can afford, it is tremendously annoying to have to discard loot that could be sold because you don’t have space for it because of random stuff or quest items.
First of all, if you want to race to 90 you miss a tremendous amount of lore and dynamic character development (including professions, gold, honor, etc.) But you can access what WoW is really all about, endgame PVP and PVE content.
Having said that, if you are new you may want to take your time leveling your first character to learn how the game works, get the rotations of your class down, and learn what to/not to do within the game. I recall when I first started playing back in Vanilla the whole feel of the game was so epic and massive. I don’t know if I would have traded that experience for anything, but the game has grown and changed a lot since those days.