Warrior vs. mage was originally touted to be the most unbalanced fight in the game (besides perhaps mage vs. SL lock). Today warriors have some new tools to fight an unprepared mage, but if you know what to look for they should still be mostly free kills for you. Let's go over a checklist of moves that are relevant to mages.
Intercept
Cooldown: 30 seconds
Stance: Berzerker
Rage cost: 10
30 second cooldown base, 20 seconds with talents, 15 seconds with PvP 4 piece set bonus. You should generally assume they have a 15 second Intercept to be safe. Fortunately, Blink is 15 seconds base. If you Blink immediately as they intercept, you will be able to Blink out of their next attempt. Rank one frostbolt following the Blink, and you can go into kite mode. You can also exploit your knowledge of Intercept cooldown equalling Blink cooldown by watching your Blink timer. As soon as it gets near being ready again, you know the warrior is probably going to try to intercept. Blink is sadly on the GCD as well, so remember to not cast for a moment when you think the warrior is going to try and intercept you for an instant getaway (i.e., you're not currently on the GCD when he intercepts, so Blink is immediate).
As a corollary, DO NOT BLINK OUT OF CHARGE. Always, always save Blink for Intercept. When the fight starts and you get charged, nova and walk away. Deal with him in other ways if he breaks the nova with a trinket.
Spell Reflect
Cooldown: 10 seconds
Stance: Battle or Defensive
Rage cost: 25
Duration: 5 seconds
With its new blatantly obvious animation, and the fact that the warrior will have to bring out a shield and switch stances, you should always anticipate spell reflect. When you see the little aquamarine shield over their head, Ice Lance to get rid of it and deal minimal damage to yourself (put up Frost Ward early in the fight when you get a chance if you really care), then continue casting as normal. Take a moment to learn the difference between Defensive Stance's animation and Spell Reflect as well, some warriors will try to bluff a reflect by switching to Defensive.
The 25 rage cost is often prohibitive. If you have them nova'd and see them take out a shield, if their rage is under 15, frostbolt without fear. Be careful for rage gaining abilities (Second Wind will give them rage when rooted, for example), so don't cut your luck too close.
If they have the rage while in a nova, and are waiting for you to frostbolt, try faking them out by starting to cast frostbolt and then ice lancing midway through the cast. Start frostbolt back up if you have time, or rank 1 frostbolt to just get the snare on them before the nova breaks.