An easy solution to an empty to corner is a standing lamp. The good news is that this will take up space in small corners while keeping the room well lit.
Probably one of the best things to put in the empty corner of a bedroom is a chair. This could be a nice cozy armchair to read in or just a small butterfly chair.
A mirror is one of the best things to put in a cramped room to magically make it feel bigger. It's one of the most basic optical illusions for interior design.
Choosing a coat rack as the thing to ramp up the space is great for those with not enough closet space.
Corner shelves are all the rage now. It's a great idea to get some of these and install them. They can be used as plant holders, a book holder, anything really.