There should be a smoke detector on every level of the house, including the basement. It's especially important that they are installed near bedrooms.
Install smoke detectors near the ceiling because smoke rises. Don't place them where a draft could interrupt their detection, including near vents, doors and windows.
Don't paint over smoke alarms--paint interferes with their sensitivity to smoke.
An optional measure is to hardwire all the smoke alarms to go off when one detector sounds the alarm. Install smoke alarms that flash or vibrate if someone who is hearing-impaired lives in the house.
Ionization alarms work best to detect flames; photoelectric alarms will sound when fire is smoldering and smoky.
Test the batteries monthly and replace them at least once a year. Some people choose to change batteries during the winter and spring time changes or on their birthday.