when you buy new items...get rid of the old.

I have a policy that my mom instilled in me when I was younger.
"however many new items you're putting in your closet, get rid of the same amount."

I have stuck with this.

You tend to forget all of our clothes you have in our closet. They are usually in the same place for years.
Once you do buy new items though, it's nice to find either similar items and get rid of the old one.
You also can just try to eliminate something that you don't wear, don't like how it fits, or just don't need.

A trick to help you with figuring out what you should donate,
start each year with your hangers facing backwards. Once you wear that item, hang it back properly.
At the end of the year if you still have items that haven't been worn, they should go.
A realization of knowing you didn't wear them for the last year should be good enough reason!

This tip & trick will also keep your closet manageable and not bursting at the seems!