If you've already used preventative flea control outside of your house, there are some additional steps you can employ indoors to keep fleas at bay.
If you already have a problem with a flea infestation, vacuum any infested rooms daily. Use the attachments to get into the corners and cracks. Dispose of the collected dust and insects daily (if possible, sealed them in a covered garbage can in direct sunlight).
If frequent vacuuming is not effective, have carpets and upholstery steam cleaned.
If your pets sleep indoors, wash their bedding frequently. Flea eggs can hatch within two days of being laid.
When you're getting a new pet, especially if you are considering adopting a stray, haven't checked and treated for fleas as necessary. Animals are one of the biggest ways fleas get into your home.
Clean uncarpeted floors with oil instead of water.