General RvR Tips
The Archmage is a unique and powerful class for many reasons, including its powerful healing and helpful utility spells, but one of the things that makes it most useful, especially in RvR, is the High Magic mechanic. The way this works is when you cast a damaging spell, you build up force, which allows you to cast healing spells faster or more efficiently, and casting healing spells does the opposite. In RvR, this is not as useful as it sounds, as you often don’t have enough time to make use of it, but it does allow healing and damage spec’d classes to throw out powerful heals or nukes. No matter how you play your archmage, use this to your advantage. An instant Blessing of Isha or Radiant Lance can make a difference, so be aware of your High Magic. Also, make sure you learn to use Walk Between Worlds. This ability reduces incoming damage by a significant amount, and when combined with lambent aura or shield of saphery, it can allow you to escape otherwise life-ending situations.
Path of Isha
When playing the Path of Isha, the Archmage is most suited to a support role. While at this current point in time, some game imbalances have made Warrior Priests better healers in volume, Archmages still have extremely powerful healing tactically and overall. For the first twenty levels, you will want to try and keep Lambent Aura and Healing Energy up on as many of your teammates as you can. Your large heal is slow and easily interrupted, so you want to preempt as much damage as possible with HoTs. Once you reach 20, you should give preference to Blessing of Isha - don’t spam it, unless it is necessary, and if you need to, make good use of Drain Magic (which sucks action points from your enemy and will benefit from the Tranquility you’ve built up). Don’t be afraid to use your damaging spells, especially if you’ve built up a lot of Tranquility. Sometimes you can’t count on your allies to protect you, and with full High Magic you can do enough damage to at least discourage would-be attackers, or buy time until your allies can get to you.
Path of Asuryan
Recent buffs to the Archmage class have made playing a damage dealer significantly more viable in RvR. When playing as an Asuryan nuker, favor Radiant Lance (especially since some armor sets benefit this spell) and Searing Touch for the bulk of your damage, but make good use of your DoTs as well, as they can build up to a significant amount (and build Force quickly). Law of Conductivity, Radiant Gaze and Transfer Force are good abilities to open the battle with, and if you can, try and get at least those three on your opponents before you start nuking. Absolutely use healing abilities when your force is built up - an instant Blessing of Isha or Gift of Life can be a game changer, and with full force, Shield of Saphery can protect you from even the most enthusiastic attacker. Once you get Feel the Winds, the x9 ability in the Asuryan tree, use it liberally, along with Storm of Cronos, as it will massively increase your damage. Play to the outside of the main battle lines, and try and pick off enemy casters. This will become even easier when you reach level 35 and learn Law of Gold.
Path of Vaul
If you want to play a “twisting” Archmage, making full use of your hybrid abilities by switching back and forth from healing to nuking as the situation calls for, then the Path of Vaul, combined with points in the other masteries, may be a good choice for you. You can also easily play as full damage or full support, though your abilities lend themselves to the latter. Until level 18, play as you normally would, but when you get Rain Lord, you will start to take on your full role as a debuffer. Soon you will have Law of Age, Stom of Cronos and Mistress of the Marsh, and you should give these abilities preference and use them liberally, as no other class can reduce the effectiveness of his enemies and increase the damage of his friends better than the Archmage. Use your debuffs in chokepoint situations, paired with nukes and heals as you see fit. You are especially useful in keep sieges, where you can slow down or help defeat an enemy zerg with your debuffs alone. Use them wisely.
With the new Archmage changes coming up, you may wonder if this is all going to be relevant in a few months. There is no way to tell, but it is fairly certain that the Isha and Asuryan lines, in terms of focus, will be unchanged, and you will be more able to play as a nuker or healer as you see fit. As for Vaul, it appears that the abilities are being spread around and some new ones introduced, but you will still be able to play as a debuffer and support Archmage if you so desire. So choose the path that most fits your temperament, and go to work. The Archmage is an extremely powerful class, if played correctly, so stick to your guns and go for it.