Frost death knights wield two one-handed swords and can be on top of the charts on single target DPS on some fights. In high mobility fights it can prove to be a challenge to maintain that DPS. Two hand is not viable on this expansion.

Rotation for Frost Death Knight Wotlk

Frost Death Knight Rotation and Priorities

Diseases (Icy Touch/Plague Strike) > obliterate > Frost strike or Howling Blast(Rime procs have priority) on Killing machine proc > Frost strike to dump runic power > refresh diseases with pestilence

Tips

Never allow diseases to drop, most of the damage from abilities drop without diseases.

Get to know the fights to pop cooldowns at the best times (low movement, no crowd control, AOE, etc).

Time cooldowns so they can be used to clean thrash and be ready at boss fights.

Know the presences, frost can help if there is a lot of incoming damage, unholy boosts the DPS on high mobility bosses (ex. Professor Putricide), and Blood presence gives the highest DPS in low movement fights. Timed well unholy presence can be used to reduce distances and swapping back to blood presence in the right moment can increase the overall DPS, however knowledge of the boss fight is needed to not incur in a DPS loss, has runes will have to be sacrificed to swap presences.