1. Reduce screen brightness
2. Turn off wifi and gps when you dont need it. Use the power control widget.
3. Goto Settings>Wireless & networks>Mobile networks and enable “use only 2g networks”.
4. Disable auto sync. Go to Settings>Accounts & sync and uncheck Auto-sync.
5. Turn off vibration mode.
6. Do not use too many widgets on home screen.
7. Avoid using live wallpapers.
8. Check battery usage of apps. Goto Settings>About phone>Battery use. Some defective apps use more battery power to run. Remove such apps.