I've worked in many places - confined areas, basement, public areas and open space and found I enjoy painting in my own work space at home away from distraction of daily life with lots of natural sun light. Indoor lights can give the wrong sense of colour so most of my paintings are created during the day time with the sun shining through the windows.
I always use an easel, never a table and I try to paint in a large room so I could examine my painting from a distance and from various angles. When painting a portrait or at that matter any other art piece, it's very important to observe your work from as many angles as possible.
Music is also added to my environment -another important part of my world when painting. It lifts the mood and puts one in the creative state of mine.