Altfactory, a player of multiple classes, has played off and on since original World of Warcraft. Predominately, playing horde has explored many classes and specs.
Tips that might be useful from my experience:
Find what is valuable to your class and spec. Little things when you are at end game such as equipping the wrong stats will tell others what your skill level is. Learn the talents and spells you have in your arsenal, people often die or have issues because they over look something useful.