1. Turn things off.  If you’re not using Wi-Fi then turn it off.  Same applies to Bluetooth.  If you’re out of your coverage area you can even turn off the cell radio so you’re not drawing down the battery.
2. Disable programs that use a lot of resources.  The navigation program and other location-aware programs can turn on the GPS receiver frequently.  Instant Messenger applications use the network.  Turn off those programs when you don’t need them.
3. Decrease the frequency of e-mail checks.  If you can go longer between e-mail checks you can extend your battery life.
4. Use Wi-Fi rather than the cellular network when possible.  Wi-Fi uses less power than than the cell radio so grab onto a Wi-Fi signal when you need to access the Internet.
5. Reduce screen brightness.  The backlight on he display will draw some power so, if you can live with a dimmer screen, turn it down some.  To adjust the screen brightness use the Screen and Lock app .  Tip:  From card view type ‘sc’ then click on Screen & Lock.  Use the brightness slider to adjust the backlight.
6. Pick up the 1350 mAh battery from from Seido.  This larger battery fits into the Pre without modifying it and gives you 20% more battery life.
7. Plug in whenever you can.  Get an in-car charger for trips where you’ll be using the turn-by-turn driving directions and use the charger at the office or at home.

If you’re stuck somewhere without your charger and you know you’ll need your phone later you can completely power down the phone.  To power off completely press and hold the power button until a menu appears (about five seconds) then choose Power Off.

For more information on saving power check out this PreCentral Article and this PreCentral forum post.