Str is the only attribute for unholy DKs. For additional stats, get hit capped first then worry about haste, crit and finally mastery. Tips would include speccing correctly, keeping your ghoul always up and keeping diseases rolling on the mob. Check out Elitist Jerks website. Here is my dk for reference on what to spec, gemming equipment, etc. Take it as you will.
http://us.battle.net/wow/en/character/lightbringer/Meerette/simple