The replies here are very good. I have a few comments to add, though. If you are tanking HM FL, you should ignore this advice -- but I do not think you would be posting here if that were the case.
There's a lot of weeping about how avoidance 'penalizes' us since it reduces our damage taken, weakening Death Strike/Blood Shield. I would in fact like to see slightly different Death Strike functionality, but this is generally untrue; avoidance works in concert with Blood Shield, since every hit avoided is another one that does not weaken the shield. On a very abstract level, you can think of your avoidance as improving your Blood Shields by whatever your total % is. So, for example, 33% avoidance is like having a 33% stronger shield (that is, it will be absorbing damage 33% more of the time). Stacking shield is better than letting it time out, so DS at at most 8-second intervals while you have shield left.
The shield is also directly improved by Mastery (always) and Stamina (usually). Avoidance stats have diminishing returns; Mastery does not. Stamina/maxhealth affects a number of our abilities besides DS, and is generally important to have. This places us in a slightly delicate position of stat balancing. Given how much easier it is to get Parry than Dodge most of the time, my reforging priority is:
- Cast Horn of Winter to get more accurate defense stats before doing any reforging. Also get Mark of the Wild or Blessing of Kings if possible.
- Never reforge out of Dodge or Mastery.
- If Parry is higher than Dodge, reforge Parry into Dodge or Mastery (whichever is not on that gear item.)
- Reforge Expertise, Hit, or Haste (which should only be on your weapon) into Dodge if possible, or Mastery if not.
- Replace any gear with Crit. If you really can't get anything better than a Crit/Mastery weapon, complain about it on the forums, then reforge as you would Haste.
As for enchants and gems: Contrary to some earlier posters, I strongly recommend mixing Stamina into anything possible to do so. In general, aim for your Mastery to be 1/10,000th of your total Stamina unbuffed in Blood -- so 170k hp <=> 17 Mastery (about 1600 mastery rating). This isn't a magic number so much as an easily-followed rule of thumb; the math for the actual 'best' is a hot mess, and depends on fight, and I don't want to get into it. This'll keep you close without needing to break out a calculator every time you move to a new boss. If you don't have some very good Stamina trinkets, this may well mean gemming Solids in blue or prismatic slots or using an armor kit over the mastery glove enchant. Before you go that far, regem yellows as Puissants and see how close you are. Explaining blue gems to your healer can be a headache.
Chest : Greater Stamina. (+75 Stamina) Three of the five stats from Peerless are worthless to you and 20 Strength is not worth the 55 additional Stamina.
Boots : Earthen Vitality. The move speed bonus, small as it is, is essential, even if you have Glyph of Bone Shield, and more than worth the 14 lost stamina from an armor kit.
Food : Have it and use it. I highly recommend you level cooking and learn at least these three recipes : Lavascale Minestrone (http://www.wowhead.com/spell=88025), your best food; Mushroom-Sauce Mudfish (http://www.wowhead.com/spell=88031) for second-best; and one of Grilled Dragon (http://www.wowhead.com/spell=88020), Crocolisk Au Gratin (http://www.wowhead.com/spell=88014) or Beer-Basted Crocolisk (http://www.wowhead.com/spell=88005) as a throwaway, since the meat is so easy to farm for either and the non-Stamina part isn't a complete waste. The third is my preference since it's the only one that improves survivability, and it buffs from MotW/BoK.