Fill up a few bowls or pie pans with about 1/2 tsp. each of dishwashing liquid, and fill up the containers halfway with water. Stir to dissolve dishwashing liquid.
Place these containers around your floor, either under nightlights or under a lamp.
Sprinkle salt from a salt shaker around your floor, and it let sit in place overnight. The salt will dehydrate the fleas, and while in search of an escape the fleas will typically jump into the dish soap. The soapy water smothers and kills the fleas instantly.
Discard the soapy water the next day and vacuum your floors thoroughly. Use a vacuum with a disposable bag, because this will collect and trap the fleas and the salt that you sprinkled across the floor.