As mage, you won't be able to defeat other classes with range, like hunters, as you'll almost WoTLK Gold always do more damage than hunters do. In a duel, a battle with a mage is usually akin to a competition of skills and equipment, provided that both mages are on the same levels.
The main issue is when combating melee classes, particularly rogues and warriors. If you wish to have any chance of beating melee foes then you must put some distance between you and your foe. Slowing capabilities like Frost Armor can be effective similarly, as do roots such as Frost Nova. If you're in a pinch you could use Blink to instantly move out of danger or you can use Polymorph to give you time to escape any enemy who has got the upper hand.
There's a myriad of strategies depending on the tree of talent you are specialized in. The basic approach is the same. There is no issue beating ranged classes (such as other hunters, casters or other casters,). Your primary concern should be to keep a the distance between yourself and melee-capable classes (warriors and paladins, rogues and Shamans). Utilizing frost armor blink, frost nova and poly. This is an excellent method to gain away from someone who had an advantage over you.
A thing to keep in mind is that a lot of players on PVP servers will give up their pure specialization in one talent tree to gain the possibility of combining talents into two trees, typically Arcane/Fire or Arcane/Frost. In Arcane the main PVP abilities are Arcane Missiles, and Arcane Explosion. However, you'll typically need some Fire abilities to buy WOW WoTLK Classic Gold increase damage or Frost to slow enemies. It is also possible to specialize in Fire or Frost, while you can also acquire some Arcane talents to increase your versatility. The standard division is between 31 abilities in one specialization tree, and 20 talents in the other. This is because it is the minimum level required to gain the power at the seventh level on the talents tree.