The month of January is open season on scheduling vacation. If there are two people who want the same week, seniority rules. After January closes, then vacations are scheduled on first-come, first-served regardless of seniority.
Holidays are rotated. If you had Thanksgiving, Christmas, Memorial Day, etc week this year, you can't get it again for the next five years unless no one else asks for it in January.
Each person has two weeks vacation regardless of how much time they've been at the company. There is no 3 weeks for X many years, 4 weeks for X many years incentive. We each have two weeks and that's all we're going to get even if we spend 20 years at the company. Needless to say that cuts down on the time-off bickering over calendar hogging.