First group like items together but put your hangers backward. As you wear an item and hang it up again, turn the hanger around. This will give you an easy way to see what you wear and what you don't. At the end of the season or sooner take everything that is still on a backward hanger and get rid of it.
Another method is when you re-hang your clothes after wearing, hang them to the left of everything else. Shortly you will notice clothes on the right that never get worn. Unless they are special occasion clothes, your giveaways will be to the right staring you down.
This works great for kids clothes too!