These are some good tips I found from www.knowyourcell.com
Reduce the time before the screen turns off
You can set your Samsung Focus to have a shorter screen time-out duration and set your phone to lock automatically so that large 4-inch screen doesn’t drain power. To do this, swipe left to the app list and then settings. Select Lock & wallpaper to set up a lock password. Select Screen time-out from the same menu to extend the time-out duration.
Lower the screen brightness setting
The brighter you have your screen, the quicker you’ll find power drains from your phone. Select Settings from the Apps list and navigate to Brightness. Turn off Automatically adjust and select the level you want the screen brightness to stay on.
Use a dark background theme
The lighter the background image is, the more power the screen will use. Select a background image with darker colours to prevent battery power draining too fast.
Sync music and pictures on your computer
Use the Zune software or Windows Phone 7 Connect for Mac to sync your images and music with your computer. Doing this over the air can reduce battery life.
Listen to music with the screen turned off
You can do this by pressing the power button when your music is playing.
Turn connections you’re not using off
You only need to have Bluetooth and Wi-Fi on when you’re using the features. You can turn them off in the Settings menu.
Be careful what you’re synching
Having push email turned on permanently can use up a lot of power, especially if you’re downloading large files. Change the sync settings for your email accounts to a longer interval. To do this, select Settings from the Apps list and choose Email & accounts. Tap the account you want to change, select Download new content, select a longer interval, followed by Done.
Me and People Tiles
Each time you visit the Me and People tiles, your phone will use power to update the streams. Try to limit how often you open these tiles.