First, take down pictures and ornaments and store them somewhere safe.
Move your furniture into the middle of the room to allow you to move around more easily.
Cover your furniture with a clear plastic sheet so you and your family can see what’s underneath and aren’t tempted to put things on top of it.
A clean dustsheet will protect the floor from paint and create a non-slip surface if you’re using a ladder. Look for a dustsheet with a plastic backing, as this will be much more effective against spillages.
If you have carpet, you’ll need a bit of extra protection. Use 5cm wide masking tape around the edge of the carpet, overlapping slightly with the baseboard. Use a paint scraper or a sharp tool to push the tape down under the baseboard.
Use masking tape to cover such things like door handles and knobs.