About playstyle:
There is really not that much to look out for in the "new" Gruul-fight. Run in, let the tank get a Sunder Armor off and start nuking with Arcane Blast/Arcane Missiles. Wand two times when you're hit by Reverb. Immediatly move out of Cave-Ins and do this intelligently: don't run zigzag and rather look where the Cave-In is coming from and where it is moving to. On Ground Slams, blink if you're getting kicked into a bad place in the Lair. What do you need a safespot for since the Shatter is hitting for so much less damage? If you have a SPriest and maybe a Shaman in your group, run with a 3 AB-rotation and use Molten Armor. If not don't be scared to use Mage Armor and rather do the 2 AB-rotation. It will greatly benefit your mana regeneration. If you have spare mana at the end of the fight you can still Arcane Blast-spam until you're OOM.
I'd go with 2/3x AB, 1x AM, 1x Scorch-rotation. Use /Stopcasting-Macros for those spells and get used to it (maybe work with a special castbar like Quartz).
Also try to use Arcane Power/PoM as soon as possible so you can use those timers 2-3 times during the fight.
About your spec/gear:
You should always have an idea what you're speccing/equipping for. Currently you're leaning towards Arcane but lack one point in Arcane Focus. You could swap your Scryer's for something like Icon or Shiffar's if you pack that last point into Focus.
So you have two nukes that are getting supported by your talents: Arcane Blast and Arcane Missiles. Putting points into another element now to support your Arcane-Blast rotation is a good idea. For good rotations Scorch is the more versatile spell, IMO. You would want to get Ignite then so your criticals do a really good amount of damage (that's actually the biggest flaw in your current spec). Elemental Precision is alright but you should also try to get Incinerate. Improved Fireblast is not necessary nor is Flame Throwing - you'll have to stand near the mob to cast Arcane Blast/Missiles anyway. Pyro for AP/PoM is nice. Your equip is looking good damage-wise though you're lacking spirit. You might want to grab the next T4-shoulders from Maulgar.
