Well, since you are a tank, you'll need to get your defense up to 535, to make you uncrittable in heroic 5 mans, and to 540, to make you uncrittable to raid bosses. Get your rep up with the wyrmrest accord first, so you can buy their cloak, boots, and chest, all of which will give you better defense rating than the items you currently have equipped in those slots.
Then work on argent crusade rep, for the special issue legguards, and then kirin tor rep for epic gloves. Also check out the enchants that you can get from the rep vendors, shoulder at sons of hodir, head enchant at argent crusade I believe.
Also, enchant all your gear for defense. Titanweave gives 16 def to your cloak, there is a 12 defense enchant to bracers. Once you have reached the 540 def mark, start to gem for dodge, expertise, and stamina. Run heroics for gear drops, HoL for the shoulders, CoS for the bracers, and place defense enchants on them. Regular HoS drops the eternally folded blade from the second boss, and the infantry assault blade drops in heroic UK, I believe. Once you have enough emblems of heroism, buy the emblem belt, and place a buckle in it, so you can have two gems in it.
As soon as you reach 535 defense, run heroics night and day, to gear up. A nice tanking ring, epic, the keystone great ring, drops from the last boss in heroic dtk. The red sword of courage, drops from the last boss in heroic UP.
After thet, go to naxx.
Tom