No multi Glad here, but maybe it helps some new Mages to reach their Eliteset this Season.
-Trade your Blink/Shimmer against Gap-Closer like Warriors charge.
-Don’t push! If there is no opportunity to secure a kill just keep your distance. When a gap closer is ready and the melee already sticks on you, try to gain some distance first with frostnova and slows
-If you can Freecast from distance= do it 
don’t waste time on running around, when u are already in a good position. When u are forced to move to build distance, use your instant Casts for your advantage, even a Fireblast while running is better than using no global Cooldown at all.
-Support your Team mates: peel when your healer is in CC with a frostnova, Polymorph a Dps or disturb a rogues Smokebomb with fire nova or ring of frost.
-Use mirror images before an Unholy Deathknights burst to avoid the grip
-Don’t polymorph the enemy healer if there is no pressure from your team at all. And most important, don’t waste polymorphs Diminishing Return. I see a rogue sap or a mage polymorph so often, even when nothing is happening at all at the opener. When u open from Stealth with a CC, put some pressure on and use your opportunity.
-Get your counterspells on point: the enemy healer gets out of a CC and he really needs to cast a heal to safe his mate, that’s your moment. Make his life even worse than it is at that point.
-Don’t underestimate the power of “slow” or Ice Wall at Blade´s Edge Arena after a good fire nova. (Fire nova on an expiring polymorph is always a good way to annoy)
-Use Ring of Fire or (lil bit worse) polymorph , to bait interrupts. You don’t wanna get kicked on frostschool.
-If you play for example with a rogue or warrior, time your burst with his Kidney Shot or Stormbolt. Bursting together is more effiicient then a single one.
-The enemys Healer is in a bad position and next to you? keep him there while his mates were out of sight with a fire nova/frostnova and slow.
-Bait melees into bad position, especially when you have everything ready to blow them up right there.
-Save enough Mana to Spellsteal important stuff, like Paladins BoP. Don’t start a spellsteal race with a Druid. -Rebuff Int against Shamans/Mages and Priests.
Good luck fellow Mages and upcoming Hogwart students.