Cleaning walls of spots and dirt the day before you start painting is a smart idea. When you spot clean a wall it is best to let it dry for one day before you paint.
Then when painting an entire room you’ll want to take logical steps. First remove all the furniture or pile it into the center of the room and protect it with a plastic tarp or sheet. Second you’ll want to use blue painters masking tape to protect any trim from spatters or stray brush strokes. Next you’ll want to protect the floor by taping down a tarp, sheet of plastic or trash bags taped together.
Start painting the ceiling first, then paint the trim, windows and doors, then the walls. Make sure you let the paint dry in between each step so you don’t mess up the work you just did. Check the cure time on the can of paint to allow plenty of time for the paint to dry before removing painters tape and starting the next step.