Retribution is the recommended leveling spec before level 30, and is still very good for leveling purpose after that. When leveling as Retribution, using a two-hand weapon and dealing with one mob a time is recommended. Below is the most efficient talent build for leveling your character:
Level 10-14: 5/5 Benediction
Level 15-16: 2/2 Improved Judgement
Level 17-19: 3/5 Deflection
Level 20: 1/1 Seal of Command
Level 21-25: 5/5 Conviction
Level 26-28: 3/3 Pursuit of Justice
Level 29: 1/3 Crusade
Level 30-32: 3/3 Two-Handed Weapon Specialization
Level 33-34: 3/3 Crusade
Level 35-39: 5/5 Vengeance
Level 40: 1/1 Repentance
Level 41-43: 3/3 Sanctified Judgement
Level 44: 1/3 Sanctified Seals
Level 45-49: 5/5 Fanaticism
Level 50: 1/1 Crusader Strike
After Crusader Strike is obtained at level 50, you should be able to solo efficiently however you spend the rest of the points. You may also consider respeccing to other more typical builds when you start joining instance group or battleground regularly.
