Spell Hit and Raids
The hit cap for raid bosses(skull mobs) is 17%. With 17% you will have a zero chance to miss. There used to be a 1% chance to miss that you could never circumvent, but this is no longer the case. You can now achieve 100% hit rates.
Common Hit "Goals" (always rounded up)
17% - 446 Hit rating
14% - 368 Hit rating
11% - 289 Hit rating
8% - 210 Hit rating
1% of Hit is equal to 26.232 hit rating
It's pretty easy to figure out how much hit you need. Check your talents, subtract that from 17, do you have a shadow priest or balance druid providing a debuff? Subtract that. Viola! The rest is what you need from gear/gems/food.
Almost every gear or talent question can be answered by using Rawr. For more info on using Rawr including where to get it and how to set it up properly, read THIS thread. What stat is better for x spec or what piece of gear you should use can be answered by Rawr.
SimulationCraft is another simulator that can be used to compare different specs and classes and their performance in raids. For information on that, read THIS thread.
Vontre's Magegraf rounds out the simulators that I know about. For information on his, go HERE.
FB(18/53/0) and Arcane(57/3/11) are very close in dps theory wise, although heavy on mana use and FB can vary a bit based on the randomness of crits and hotstreaks. On shorter fights arcane tends to have a bit of an advantage. FFB(0/53/18) is about 5-6% behind but a lot easier on mana although varies wildy on DPS due to the huge crit multiplier combined with hotstreaks. Frost(18/0/53) is behind FFB and not really competitive at the moment.
FB requires the most hit from gear with none from talents.
FFB is next along with Frost getting 3% hit from talents.
Arcane requires the least hit from gear getting 6% from talents.
There are great threads on both FFB(FB is basically the same) and Arcane that you should check for information on rotations, glyphs, consumables etc if you have a question about them.
Mirror Images drop your threat significantly below zero for 30 seconds when cast, REGARDLESS of whether or not the images remain alive for the whole duration. Check THIS thread for specifics.
Mirror Images are useful for aoeing adds because they allow you to go all out with AOE and not worry about pulling aggro and also as a temporary threat drop .
Ignite "Munching or Rolling"
While sometimes you will lose ignite damage with back to back crits that land close together (like a HS Pyro after a FB/FFB) you also sometimes gain extra ignite damage. Basically don't try and avoid ignite munching by scorching before using HS procs or otherwise delaying them, its not worth it. Just play as normal.
Tips and Tricks:
This macro in combination with good raid frames has been invaluable for me on fights where I have to decurse:
/cast [target=mouseover,help] [target=player] remove curse
All I have to do is mouseover whoever is cursed and hit the macro without having to click on them.
In addition, there are many fights where Blink can save a lot of time if you get knocked into the air. If you are over flat(ish) ground, using blink will immediately move you back to the ground when you are airborne. This was always useful on fights like Archimonde where I never had to worry about slowfall or using tears and could go right back to dps.
Switch targets early on trash or boss fights with multiple targets if your spell would not land before the mob dies so you don't waste a cast.