In order to protect your floors from spatters and stains, place a protective plastic sheet over the whole surface, covering the floor – corner to corner. If the baseboards don’t need masking, simply tape the edges of the plastic to the floor. If you need to mask baseboards, apply a masking film, and tape the edge to the plastic sheets that are on the floor.
Protecting the floor should always be one of the first steps you take when prepping a room for painting. However, in case a stray drop of paint does manage to fall onto your floor, have a damp cloth or paper towel handy to wipe off the paint while it is still wet in order to have a better chance of removing it without damage or staining.
Find more information on prepping a room for painting here.