I've got a few strategies you can try.
Put as much as you can onto hangers, but face all the hangers backwards, with the hook going away from you. Each time you wear something and put it back on the rack, flip the hanger. Then you have a visual of what clothes you're actually wearing. Set a time frame- maybe 2 months? At the end, box up everything you don't wear.
Count your stuff. This is really helpful for realizing how many items you actually have, and I think it's pretty fun. Clear off your bed and make a pile of shirts, a pile of sweaters, pants, you name it. It might look daunting. Grab a pad of paper and tally up how many of each cut of clothing you have and perhaps come to the realization that you don't need 17 hoodies (as in my case).
The bare-bones method. This is similar to #1, but will help with initial clutter. Just take out all the clothes you know you love. It could be as few as five or six things. Hang them up. Sort everything else into a couple boxes. It will probably be easiest to organize them by type (t-shirts, dress shirts, pants, etc). Make sure to label them! As life goes on, if you want to wear something from one of the boxes, take it out and hang it up. After a while, there will probably be quite a few things you never seem to take out of the boxes. Set a time frame. Donate them.
If all else fails, just do some research on minimalism. There are ton of ways to pare down what you own. Good luck!