First things first: NEVER stop learning. This is the most important thing I can stress, the moment you approach every situation the same as you always have is the moment you have already lost.
Situational awareness is more than key to successful PvP, there's a reason people leave the combat log open. The moment you see words like "Mikkos gains steath" and "Mikkos gains overkill" you have learned two things before the fight even starts: it's a rogue, better yet it's an assassination rogue. You won't learn if he is full 51 point assassination, 41/5/25 mut/prep or 44/2/25 master poisoner/prep until the fight begins but you'll have a slight upper hand in knowing what you can do to make the fight easier on yourself. For a good example of situational awareness, take a look at the opening scene of Rifle lovin' 12 on IQD.
Prediction and Reaction are footholds of PvP. It's the fine line between being juked (fake casting) and interrupting a cast. reacting, such as a rogue interrupting with gouge when a kick was juked or a hunter feigning death to drop target from a hostile casting opponent when your viable sources of interrupt are on cooldown. Prediction is merely knowing when something will happen and doing something about it before it even happens. Example: while running feral/rogue with Blarr on his druid we faced priest/rogue, Blarr found the rogue while i sapped the priest. As the sap wore off i began to stunlock the priest through the normal cheapshot into 6 second kidney, the rogue was dying so the moment the kidney shot ended I kicked. As I kicked I interrupted penance before a single tick went off, locking out the holy school for four seconds and giving me time to gouge as the rogue died. In this example we'll find several things, the priest had a choice to:
- penance to save his partner
- psychic scream me off and let his partner potentially die
Predicting where someone will go is a powerful tool in all aspects of PvP, shooting freezing arrows onto warlock portals and putting up enough pressure to force them to port into it, or to an awaiting teammate to finish the job.
Synergy and Communication are cornerstones of a successful team. If you play with someone who doesn't compliment you at all you're asking for trouble. Example: Hunters and mages don't seem to jive well due to all crowd control (CC) effects share a diminishing return (DR) making full control and the ability to take down someone in the duration of CC very hard to accomplish. The reason survival / destruction worked so well was the complete lack of overlapping CC (other than freeze traps/wyvern and banish). His curse of elements debuff aided in my burst and my mortal strike aided in his.
Communication was key as well, announcing durations, what you're going to do and DRs (full/half/quarter/immune) aids in the victory. If you plan on playing with someone, duel. ALOT. You pick up subtle nuances in gameplay, how they react to things and how they make decisions. You'll get to a point after playing with someone long enough that you begin to predict what they'll do next, it's happened with Blarr and with my former (and favorite) healer Togori.
Lastly, Take time to familiarize yourself with the other classes, their mechanics and how they effect you. I learned the hard way that warrior disarm now effects ranged awhile ago, after eating a ten second disarm and having my face handed to me on the end of an axe made me start reading more patch notes than just ones that pertain to my own class.
Here's to hoping this helps someone in some small way.