Selling property, how tidy should it be? what should and shouldn’t be on display?

I am trying to sell my flat and I’ve been told I have too many things in my flat. It is tidy but I have things like ornaments, boxes and extra things around my flat. When you sell property is it better to have a simple look with all clutter hidden away and the whole house to look simple and kept to a minimum. Or does it not matter and it makes no difference if you have lots of things on show??. As long as it’s clean and tidy I think are the most important things.