Kakashisan's How Not to suck as an 80 Mage Guide
Well basically, this is very simple. If you have an 80 Mage and think you just aren't living up to your potential, there are many things you can do to fix this. First of all, make sure you have the right gear. You want to make sure you're geared appropiately and that you're doing decent DPS. This, however is for PvE. You want to make sure you have ran heroics and have atleast 1400+ spell power before you try anything big. This is basically self-explanatory. Get the right gear, find an appropriate rotation and have the correct talent build.
Talents: Talent Calculator - World of Warcraft
That's a good spec for PvE.
Your rotation should be just like this: Scorch, Scorch, Scorch, Scorch, Scorch(to get the 10% crit chance up), Living Bomb, Frostfire Bolt, Frostfire Bolt, Frostfire Bolt, Living Bomb when it runs out and Scorch when the effect is about to fade, rinse, repeat. Use Pyroblast whenever Hot Streak is up; if you don't take advantage of the instant cast Pyroblast you won't max out your DPS capabilities.
That's it for PvE really and make sure to listen to your raid leaders on specific boss fights.
There's a whole different guide for PvP mages and I find them to be a lot more fun.
They're basically a pew-pew class that will take out any class in under 5 seconds given the fact they have their CD's up. Talent builds affect them a lot.
Here's a nice talent build: Talent Calculator - World of Warcraft
Something along the lines of that with your own little zest for personal preferences.
It's basically a Presence of Mind + Arcane Power + Pyroblast trick. Followed up with an Arcane Barrage and/or Fire Blast along with some other instant cast spells that you may have up. If that doesn't kill them and they're a healing class, make sure to counterspell them right when they're about to heal. Kite them with Slow if they're a melee class till your Arcane Barrage or other instant cast spells are up. Basically, the scheme is to PoM + AP + Pyro and then Arcane Barrage + other instant cast spells while kiting if they aren't dead by then. Make sure to have trinkets to deploy if you're stunned or need some extra spell power.
A much more advanced guide will be released very soon with scenarios with every single class, along with detailed boss fights and what you need to do during them.