Glyphs

If you are unfamilar with any of the glyphs available for mages, or even if you just want to refresh yourself, then have a nosey at the Mages & 4.2: Glyphs article.

Prime Glyphs

Glyph of Arcane Blast: As Arcane Blast is the main spell you're going to be casting and the spec mechanics work entirely around this spell and its corresponding buff stacking then this glyph is pretty vital.  It increases the damage from your Arcane Blast (the one spell you will cast over and over again regardless of rotation phase) buff by 3%.  Seriously, this isn't a choice, it's compulsory for any Arcane Mage.

Glyph of Arcane Missiles: Arcane Missiles will be the second spell you use regularly in your rotation, although not as regularly as Arcane Blast.  It increase the critical strike chance of your Arcane Missiles by 5%.  During the course of your rotation you will use Arcane Missiles to wipe your Arcane Blast buff (I'll explain in the rotation section if you're not familiar with this) far more often then you'll use Arcane Barrage which is typically the option of last resort.  Therefore increased crit hits from this glyph is going to be far more beneficial to you in the long run than a static damage increase afforded by the Glyph of Arcane Barrage.

Glyph of Mage Armour:  Your Mage Armour regenerates 20% more mana.  This is important for trying to maintain being 'mana neutral' (or close as dammit) during the conservation phase of your rotation ie. not spending more mana than you're regenerating in order to maximise the bonus from your Mana Adept proficiency.  Until such time as your mana pool is that large that you can afford to dip on mana regeneration (and I can assure you that's probably not during this tier) then this glyph is another compulsory one.

Major Glyphs

Glyph of Evocation: When you cast Evocation it regenerates 40% of your health in addition to the normal mana regeneration of the spell.  This is pure win in my book and will help take some of the pressure off the healers during tough boss fights.  Of course this means that you have to let your healers know that you have this Glyph and that you'll be using Evocation at the end of your Burn Phase in the rotation; being part of a good raid team is about good communication.

Glyph of Arcane Power: When Arcane Power is active it reduces the cooldown of your Mana Shield, Mirror Images and Blink spells to zero.  Although you're probably not going to want to use Mana Shield where you can avoid it and the use on Blink is situation, the reduction of cooldown on Mirror Images can provide a really nice damage boost.  Mirror Images has a relatively long cooldown, so use of this glyph may mean that instead of getting to cast it once during the fight, you could cast it multiple times.  Just be careful in macro'ing Arcane Power and Mirror Images into one button, apparently it bugs and you don't get the benefit of the glyph.  It might be worth hitting your WTFNUKE button (with Arcane power macro'd in it but Mirror Images not macro'd) then hit Mirror Images afterwards.  If someone knows a better way of macro'ing I'd love to know, just mention it in the comments.

Glyph of Blink:  There aren't many other options for major glyphs so I tend to plump for Glyph of Blink.  It means you Blink for an extra 5 yards, combined with the Improved Blink talents this does start to boost your mobility.  Anything that allows you to move as fast as possible and then seetle back into your rotation as quickly a possible is a good thing in my book.  I think you could easily replace Glyph of Blink with something else if you wanted to, I just don't think there are any better options for an Arcane Mage and personally I value the mobility.

Minor Glyphs

Personally I choose the Glyph of Arcane Brilliance, because it reduces the mana cost of Brilliance by 50% which is a small advantage if you have to buff someone who has been combat ressed; Glyph of Slow Fall, because it saves on bag space by negating the Light Feather reagent for the Slow Fall spell; and the Glyph of Mirror Images, which makes it look like your mirror images are casting Arcane Blast rather than Frostbolt which just looks better to me.  To be honest though, minor glyphs are entirely a personal choice.

I have seen it said that you must take Glyph of Mirror Images because the change to making the images cast Arcane Blast increases DPS due to the stacking mechanics; this is absolute bullshit.  Blizzard have stated that minor glyphs are designed to be either cosmetic or conveniences changes (ie. reducing mana cost of buffs, increasing the duration of buffs, removing reagent requirements to free bag space or making cosmetic changes such as turning Polymorph: Sheep into Polymorph: Monkey cos hey... who doesn't like monkeys???).  Granting a damage boost through Glyph of Mirror Images would make the glyph different from every other minor glyph in game and fly in the face of Blizzards' stated design intent with minor glyphs.  By all means use the glyph, personally I love the glyph, but don't feel like you have to.  It will not give you any damage boost.

Why Don't I Use This Glyph?

Glyph of Arcane Barrage: At first glance the Glyph of Arcane Barrage seems like a better option than Glyph of Arcane Missiles because it gives a flat 3% damage increase to the spell.  However, in your rotation you will be casting Arcane Missiles far more often then Arcane Barrage.  In fact Arcane Barrage is the spell of last resort (ie Arcane Missiles has not procc'd and you can't expend the mana to cast one extra Arcane Blast to get Missiles to proc, then you'll cast Arcane Barrage).  Because of the this, the increased damage from more Arcane Missile critical hits far outweighs any increase in damage from Barrage.  Similarly you could not afford to replace the Glyph of Arcane Blast (Arcane Blast is your main spell and the one you will cast most often, the damage increase the glyph provides is just too valuable to replace) or the Glyph of Mage Armour (you need to maintain mana regeneration in order to maximise the bonus damage from your Mana Adept proficiency).  there are just no other options to stick this glyph in anywhere if you want to maintain peak efficiency.

Glyph of Molten Armour: At first the increased critical strike from this might sound tempting, but you will not be using Molten Armour.  Ever.  Mage Armour is just too important in terms of your mana regneration and corresponding damage output to replace with any other armour during a fight.