There are a few reasons why should one take a mage to his raid group.
The average mage can
Most mages can probably do number 1 & 2, yet number 3 requires a bit more of experience, tactical thinking and preparation.
- Buff the raid
- Provide the raid with unlimited units of meals (Now that food/water is combined in one)
- Deal insane amounts of damage withing a perfect time, i.e. have have an awesome DPS count.
The main thing about your mage which makes him gear dependent is his specialization. (His spec)
- Gear
Up until 1880 spellpower, I suggest you to raid with a solid 0/53/18 Frostfirebolt specialization. The spec
- Frostfirebolt Specialization
Assuming that you're hit capped (Or that you have a draenei, shadow priest, whatever else helps you lowering the required number of hit), the stats you should be looking forward to max out go in this way:
Spellpower > Crit > Haste
With a higher crit chance, you have a bigger possibility with achieving two consecutive Hot streak proccs. (Additional instant pyroblast -> Free dps)
If you are the only Frostfirebolt mage in your raidgroup, then I suggest you to take Imp. scorch glyph instead of Living bomb glyph, however if you aren't you should make a deal with your fellow mage(s) about stacking up improved scorch on your target for additional DPS on the Living bomb crits.
From 1881+ I would highly recommend you to switch to a 57/3/11 Arcane specialization. The spec
- Arcane Specialization
Assuming that you're hit capped (Or that you have a draenei, shadow priest, whatever else helps you lowering the required number of hit), the stats you should be looking forward to max out go in this way:
Spellpower > Haste > Crit
I prefer haste with this spec. Not only faster casting time, the bonus which lowers your Global Cooldown (GCD) is very helpful after starting a new set of attacks after an arcane barrage.
As linked above already, the FFB I used to use before is this Talent Calculator - World of Warcraft
- Talents and glyphes.
Arcane spec as follows is url=http://www.wowhead.com/?talent#of0Vfk0IzxGuMtedcZbGc0o:iNw
Luckily, WoWhead has now glyphes integrated into their talent calculator, so you see my choices when checking the links, if you do so. (If you're not sure for the imp. scorch glyph, check my explanation from above)
The choice of your trinkets: (Haven't raided since Ulduar)
FFB:
Sundial of the Exiled - Item - World of Warcraft
Dying Curse - Item - World of Warcraft (since you have a hit deficit here in comparison with arcane, if you're raid's optimized, use the Embrace of the Spider - Item - World of Warcraft)
Arcane:
Embrace of the Spider - Item - World of Warcraft
Sundial of the Exiled - Item - World of Warcraft
FFB: Scorch, scorch (or 3 more times; depending on the other Fire mages in your raid), Living Bomb, Frostfire bolt until LB blows, apply again, frostfirebolt all until Imp. scorch is about to fade, then repeat the whole thing. (Keep applying Living Bomb! Since 3.0.8/9, IDK exactly which, if the BOOM of the bomb crits it refunds mana!)
- Spell rotations
Cooldowns: Icy veins: I used to pop that whenever it is available, for a longer fight or if you're in that condition, try to combine it in that way, that when it is about to end you use evocation -> shorter time to regain mana.
Combustion: I activate it directly after the second scorch, if I'm "lucky" it won't crit -> it works just as the shatter combo. (Same goes for not blowing your Hot streak if the second scorch crits and the first frostfirebolt does - without launching off a pyro from the second frostfirebolt.)
Arcane: Arcane blast x3, if Missile barrage proc then arcane missiles if not then arcane barrage, repeat.
Cooldowns: Presence of Mind - I used to activate it to get the third arcane blast off instantly. (Since it will trigger a GCD effect I have more time to realise if the third one launched a missile barrage proc)
Arcane power: Automatically after the third arcane blast if it triggered a missile barrage, if not I wait for the first proc.
First off, I almost never use mana potions, in fact, there was one single time when doing OS3D that I have used one (Was a mistake from my side, bad positioning with the blizzard, the fire wall CAME)
- Mana management
As Frostfire specialized you shouldn't have any mana issues at all, just make sure you have your three charges on your mana gem and if needed use evocation.
As arcane you will probably have some minor issues since it costs a lot of money to do all the spells (Third ablast is about 1k mana, missiles about 1k). The golden rule is to first use a mana gem and then afterwards evocation. (I'm going with the guess that your raid druids won't give you the mana regen buff)
!! One important thing to remember, don't ever wait for your mana to drop to zero. Get an addon that shows you your exact percentage, as well as your mana deficit so you can accurely determine when to use a mana gem and when to evocate.
If any part isn't explained enough, tell me/ask I'll try to make it clearer.