Step one: Read this excellent guide.
Step two: Send yourself some trial accounts. Blizzard will let you use those for free up to level 20.
Step three: Buy a copy of Keyclone (or one of the alternatives to be fair) for each machine you intend to use. That can be as few as one machine as you can run multiple WoWs on just the one machine.
Step four: Realise you've going to be spending much of the next twenty levels looking at WoW's keybindings and macro screens