It's not good for you to have things under your bed...bad enough to be peeking to see if there's a monster lurking...boxes with stuff stored in them need to be elsewhere.
The thinking behind it is pretty obvious actually...your subconscious registers there isn't a clear space beneath your sleeping area and so your head is cluttered, which leads to scrambled thoughts and bad dreams.
Same with stacking stuff on the top of a wardrobe...that creates pressure which manifests itself as headaches and migraines...
Goes without saying your bed must never have the foot facing the door...neither should you have a mirror hanging up which only shows your top half...that makes you feel disconnected from yourself...full length mirror or no mirror at all.
Cupboards ought to be neat with everything in its rightful place...drawers ought to open and close easily without sticking...having to force drawers closed or only open them with an effort creates disharmony...
Plants don't escape...Spider plants and others which hang downwards need to be placed on a table rather than hanging up and trailing down...constantly seeing something above your head can cause depression...mobiles, crystals and wind-chimes should be hung at eye level.
Under no circumstances should you ever enter your home while wearing outdoor shoes...the dust and dirt of the outside needs to remain outside...contamination occurs otherwise and you're also bringing the worries of your working day into your home...
I did once meet a chap who made a good living from advising people about introducing Feng Shui into their homes...his small flat was a tip actually...