i only was prot from lvl 43ish on, and u said thats what your mainly looking for, so here it is:
spec wise, the only real important ones for grinding are reckoning, holy shield, redoubt, and i would take wep-spec for increased dmg.
from 43-45, grind in the pirate cove in tanaris, theres plenty of quests too.
from 45-49ish (cant remember), go to searing gorge in the cauldron...plenty of quests.
from 49-58, go to western plaguelands!!! like 99% undead! Start just next to chillwind camp, the work your way through the different fields.
53ish-56 (optional), try felwood. plenty of quests and close together mobs throughout it. especially any demons and furblogs i think theyre called.
this is just how i did it. i dont really like kalimidor, so theres prob some good spots there i didnt mention.
places NOT to go for specifically lvling as prot:
un'goro crater, i would advise against winterspring, burning steppes, didnt really try swamp of sorrows or blasted lands.
As for specs, you can find plenty of those in the FAQ and lots of posts.
Technique:
(ret aura, BoSanct or BoWis, depending on situation) avengers shield; consecrate; SoL, SoW, or SoR depending on situation...its pretty obvious which to use usually; holy shield whenever redoubt procs, sometimes more depending on how many im facing (usually 4-5 my lvl, tho i just hit outlands and plan to increase that when i gear up with full outlands gear...hoping for about 1k more health at least and some more +defense).
If you cant tell, it really depends on the situation and the player/spec too in my opinion.