I wish I had discovered this when i first started playing wow, so i didnt have to use 1-2 years figguring out how to make a good UI and find the right addons.
But.. still learned a lot from this guide, Its for pvp, but most of the addons he is showing off is very usefull in pve too!
Basic UI Tutorial (video)

I'll trow in this Keybindings guide too, witch is a must if you are planing on playing wow and not do crap.
How you can become a Gladiator: Keybindings Part I