The main door is called "The Mouth of Chi" in feng shui, as this is how the house absorbs Chi, or universal energy. When a staircase is facing the main door directly, the feng shui energy rushes up too quickly to either the lower, or the higher floor, thus leaving the main floor without the much needed feng shui energy nourishment.
The feng shui cures for a staircase facing the main door are focused on creating a feng shui set-up at the main door that will slow down the energy, focus it, and then guide it to all areas of the main floor. This can be achieved with strategically placed art, strong colors, a big plant or a vase of flowers, specific pieces of furniture or mirrors (please note that the mirror should never face the entrance directly, as this pushes the energy away from your home instead of drawing it in.) Photo: Siri Stafford / Getty Images

Comments
I’m unsure what is the “main door”? I live on the lower level w/a door. There is a front door of the home, but the LL dr is the main door to my apartment?
Your main door is the main door to your own apartment.
These tips will help:
http://fengshui.about.com/od/faq/f/feng-shui-fron-door-main-door.htm
http://fengshui.about.com/od/allfengshuibaguatips/f/Feng-Shui-Compass-Reading-Apartment-Building.htm
Cheers,
Rodika