Reforging allows you to modify the secondary stats on your gear. Use this guide to determine the best strategy for reforging your stats so that you can optimize the performance of your Frost Death Knight.
DW: Expertise (3%+) >= Melee Hit (3%) > Strength > Mastery > Haste > Crit
2H: Expertise (3%+) >= Melee Hit (3%) > Strength > Haste > Crit > Mastery
1. Check for 3% Melee Hit and 3% Expertise
If you are below 3% Melee Hit or 3% Expertise, you should reforge your weakest stats (see priority) into Hit Rating or Expertise. Do this until you are at the caps for both stats.
2. Optimize Secondary Stats
On any items without Mastery (DW) or Haste (2H), reforge the weakest stat (see priority) into Mastery (DW) or Haste (2H) as available.