How to level up fast after first 80 lvl char

help mee where to buy such gear like Champion's Deathdealer Breastplate

So you have your first lvl 80 ? that's good news. now you can purchase gear with emblems in dalaran. check the npcs to see wich one sells what.
heirloom gear (bind on account gear) is right near the vendor that sells frost/triumph gear, above the horde inn in dalaran or inside the alliance inn if you're ally.