If you're a Mage, this thread from the EU forums is definitely worth a read-- it's based on a Warlock tips thread (which I looked around for but couldn't find-- if you see it, let me know and I'll link it up for the locks) that basically ran down 100 basic and advanced tips for players of that class.
If you're a super advanced Mage, you probably already know most of this stuff. The basics are here for sure-- use Blink judiciously to move in an out of range, use Sheep to interrupt casters, and downrank utility spells in PvP. But there's some other interesting things here as well-- I play a Shaman, and my first step when fighting mages (well, right after Grounding Totem) is to Purge all those buffs off. So casting Ice Barrier during my spellcast is ingenious-- either I have to interrupt to purge, or just let the barrier eat the damage.
Especially for beginner mages, this stuff is gold. If you're in the mood for tips on how to make your mage better, check it out for sure.
Update: Here's the Warlock thread. Thanks to everyone who sent it to me. Also, apparently the Warlock thread was based on a Warrior tricks thread. Anyone seen that one?