When painting a room, I sometimes just splash the paint and start working where it lands. That of course is a terrible way to do it. There is an ideal sequence of areas when painting a room. In order of increasing priority, this should be the order in which to do it:
1. Ceilings
2. Walls
3. Trims
4. Doors
5. Windows
Ceilings are first because they are up beyond easy reach. They are harder to paint than any other area in the room. Ever heard about swallowing the frog first as your first order of business? Also, they are a large area that is relatively flat - no special painting skills necessary. Walls are next because while they can be easier to reach than ceilings, they are the biggest area you will need to paint, usually taking up more than half of the time you will be working. The trims will require detail-oriented painting and can highlight how well the wall has been coated over. Doors and windows are last because they can actually be removed, painted separately and then re-attached.