I have 3 children at home aged 6-9, all boys, and they all keep me very busy. Until recently, I worked outside of the home at least 40 hours a week and with me, I can only have 2 projects going at once. I have a sewing closet, not a room, and therefore, no where by grocery sacks and pizza boxes to put my WIPs in.
I keep a running list of the projects I want to do on some paper. I also have a electronic one here on the board for the year, so I can keep track of it. I plan and plan. I have one in the hand quilting stage, then one in the piecing stage so I can keep them separate.
When I'm close to finishing the pieced one, I plan the next one. I don't start on it until I've finished the one currently quilting. The only exception to this is when I make smaller baby quilts that can be tied instead of quilted. I'll make 2 at a time, get them pieced and sandwiched, then tied and bound. All can be done in a single weekend.
Since I don't have the room to store UFO's, I refuse to have any. If I want to start something new bad enough, I know to finish what I already have going.
I also alternate large projects with small ones. I make 1 or 2 large quilts a year, then toss many a smaller project in between. I like the feeling of accomplishment that comes when something is finally finished.
I hope this helped.