Clear out your closet
Does it fit?
Have you worn it in a year?
Remove wire hangers and plastic dry cleaning bags.
Focus on your shoes
Do they fit? Are they comfortable?
Have you worn them in a year?
Remove items like rain boots and store them in the coat closet or mudroom.
Assess the layout of your closet
Is the current placement of items working? What should you change to be more efficient? Do you need to add a few hooks?
Use every square inch.
Invest in the right kind of hangers for the type of clothing
Sort items by color and like items
Sort folded clothing by color in manageable sized stacks
If storing on shelves invest in some shelf dividers so you can easily view your stacks and they don't tumble over.
Keep items you use often at eye's view
Rotate your seasonal clothes
My out of season clothes are in cubbies on my closet's top shelf. But many people use seal-able bags and store them under the bed.