One of the best things introduced in to WoW is being able to reforge your gear. Although a great tool, reforging is a bit of a tricky thing. It fine tunes your gear, but the second that your gear changes, it becomes the first thing to change to rebalance everything. I have found through my time as a feral tank that reforging should go in the following order:
Expertise Soft-Cap > Hit > Dodge > Mastery > Crit > Haste
Now, lets make a couple of things more clear, this is the base diagram if you need EVERYTHING. Now, if you are at the expertise soft-cap and are hit capped, then you would start looking at dodge next. Some will tell you that you need to only reforge in to dodge or some will say mastery. My experience has shown me that you will always get the best results by getting that expertise and hit up to where they should be. Remember, if you can't hit them, you can't hold them and all the other stats seem to become meaningless. If you are not where you should be with hit or expertise, always reforge haste or crit in to the needed stat as these are the last stats you will ever need to worry about.
Gems are also a wonderful tool that Blizzard has given us. It really can make all the difference if you add the correct gems to your gear. Gemming should be done in the following priority:
Expertise Soft-Cap, Agility, Stamina, Mastery, Crit, Haste.
You might notice that hit is missing. You should, as a general rule, avoid gemming for hit. You can get this through gear, enchants or reforging. People will argue with me on this order, and I'm ok with that. Everyone is allowed to have an opinion. However, this order is what I have found works the best as a priority list. Remember, if you can't hit them, you can't hold them. Secondly, you will have good amounts of stam on your gear as is, getting your dodge rating up should be the highest next priority next to hit and expertise. You won't need huge amounts of health if the mobs can't hit you.
Now the biggest discussion is always "should I got for the socket bonus?". The answer is yes.....and no. Let me explain, deciding on if you should go for the socket bonus is entirely based on your stats and what you really need. For example, if you are wearing:
Cuirass of Calamitous Fate
Binds when picked up
O Yellow Socket
O Blue Socket
Socket Bonus: +12 Attack Power
Durability 165 / 165
Requires Level 80
Item Level 245
Equip: Increases your critical strike rating by 90 (1.96% @ L80).
Equip: Increases your haste rating by 90 (2.74% @ L80).
As a tank, you will most likely be able to make better use of this chest by tossing in agility and stamina gems. You could toss in some multi stat gems to get the bonus, but to be honest the +12 attack power is just very much to make it very useful to a tank as opposed to the stats you'd get some solid color gems and forgetting about the bonus.
However, if you had:
Binds when equipped
O Red Socket
Socket Bonus: +10 Agility
Durability 165 / 165
Requires Level 85
Item Level 359
Equip: Increases your hit rating by 173 (1.44% @ L85).
Equip: Increases your critical strike rating by 243 (1.36% @ L85).
You will every definitely want to put in an agility gem or expertise gem to get this bonus. The bonus is a sizable plus in a a key tanking stat that it is worth getting.
I hope this helps out and answers some question. If you have any questions or comments, please feel free to comment on here and I will asnwer them very quickly.
Remember bears, keep up the good work! We have to show these other tanking classes how it's done!