DIfferent stations for different tasks so it forces you to get up and move around AND your sewing space doesn't become a mountain of clutter (speaking from experience). Similar to a kitchen, the flow of these stations needs to work.
GOOD LIGHTING!!!! It really stinks when the light casts a shadow or glare on the ruler.
Storage to suit your personal style. I am a visual person, so having things behind closed doors gives me grief (I NEED TO SEE MY STUFF) but people who like things neat and tidy would not like their stuff exposed.