Using a wired headset can significantly cut down any exposure to radiation while you use your cell phone. Wired headsets are much better than Bluetooth devices.
Get Used to Texting
Teens are doing it more than ever. If you spend most of your cell-phone time texting or using apps, your device should remain far away from your brain.
Don't Use Your Cell Phone as an Alarm Clock
This is (literally) a no-brainer. If you use your phone to wake up, you'll probably have it close by your head for hours while you sleep. Don't.
Watch for Radiation Hot Spots
Cell phones tend to emit significantly more radiation when the signal is weak, for instance in rural areas, elevators and buildings.
Use a Radiation-Blocking Case
The good people at Pong Research sell a case that will block much of a phone's radiation for $30 to $50.