Store infrequently used objects. People tend to place things they rarely use in easily accessible spots, then complain that they have no space.
Organize a room using four boxes labeled trash, donate, belongs in another room, don't know. Place everything you don't use or look at into one of those boxes. Then toss the trash, place the donation box in your car, return items to their rightful place and put the don't know box in the attic or garage or other out of the way place. If you don't open that box in a year or six months, get rid of it.
Stop perfectionism. Don't let an imperfect situation be an excuse to do nothing. Even if you don't have time to wash all the windows, you might have time to wash one. Learn to be happy with doing things in incremental bits of time. Large blocks of time are too hard to come by.
If you feel overwhelmed, try the tidbit method. Instead of one room at a time, tackle one drawer or one corner at a time.
Organize with a buddy. A friend can be objective about your belongings and help you be more realistic.
Use drawer dividers in your kitchen, bathroom and desk, and your space will multiply. Don't forget to use containers on shelves. You can handle several things as one unit and convert your shelves into drawers, making the items in the back as visible as those in the front.