Hello!
I'm new to posting on the forum but have been reading the mage postings for months. I have been playing in AB (Arathi Basin) quite a while now and learning a lot about PvP, so I'll take a shot at answering your question.
Tactics, for the most part, will depend upon your spec. I am pure fire at the moment (lvl 47) and what I do will be vastly different from frost. So, here is what I have been doing in the BG's from my "Watch em burn" point of view.
Ambusher: I love nothing more than to see some Ally hero charging up the ramp to the lumber mill in AB while I am hidden behind a hill. If they are by themselves (for your question I am assuming 1 vs 1) and I have the jump, I target before he is in range and sheep once in range. Then, while the ally is grazing tasty grass at the gates to the underworld, I light up Pyro, chase into Fire blast range, FB, then blink TOWARD him and Blast wave. These three spells should have cooked him immediately, espcially if Ignite procs. However, If still alive, then I nova, back out of melee range and scorch until dead. If NOT dead, then my Fire Blast has recharged and he is dead then. IF the sheep breaks before my pyro goes off, (or nova) then its a new dance with new moves. Ultimately, my goal is to roast him as hard and fast as possible.
Ambushed: This all depends on what class is doing the ambushing. Last night, a rogue ambushed me in AB and I used the basic same trick to BBQ him. Once the stun was broken, I nova'd, sheeped then ran the same basic dance steps listed above. It was GG pretty quick. Until his Ally army arrived that is! LOL
Now, my play style is different. I like to mix it up and never really enjoyed flying kites. I guess thats why I chose fire. The Spirit Healer and I are good buds, too! However, if there is a large group of Ally and they are engaged with horde troops, I get in the rear and scorch/FB. That way, I get to enjoy watching enemy health fall like an avalanche and imagine the mindset of the enemy, saying to himself, "what tha...?!!!" and never knowing what or who is really pounding them.
These are BASIC BASIC BASIC. The key is be in or take control and in Douglas Adams immortal words, "Don't Panic". If you are dealing with a caster you will need counterspells, shields, etc. Be willing to use everything in your ******* to stay alive. Make sure you have your keyboard properly set up for what works best for YOU, etc etc etc.
There is so much more tactically involved than I listed and that is what, IMO, makes the mage the greatest and hardest class to play. You truly have to be the smartest player on the field, always aware of what is going on around you and ready to change tactics in a heartbeat.
I hope this helps!
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Worry is just a misuse of the imagination. Instead of imagining the worst, try imaging the best. Cheers!