One really important thing I’ve learned is that you need to tell your employer when you need time off. You never request it.
Another really important thing I learned is if you have a good relationship with your boss is to discuss or ask when it would be best for the company to take time off and try to arrange you schedule with those dates in mind.
As an example of this, I like to take a vacation in the summer so I will usually discuss the best week I can do that with my boss because it’s not very importent to me exactly which week I want as long as it’s some time in the summer.