How can I improve my iPhone's battery life?

A recent research conducted on cellphones (smartphones) revealed that most of your battery life is drained by "Internet" and "calls". The more you use your phone for any of these two, the faster your battery drains. Next on the list is "Search for network" which consumes quite a bit of your battery power.
Smaller culprits are WiFi, Bluetooth, Screen brightness, themes, Vibration, etc.
* Reduce screen brightness to minimum
* turn off WiFi/3G/4G when not required (same with Bluetooth)
* if you are out of network area, turn off the mobile network so you cell doesn't keep searching for a network.
* If possible reduce internet usage on your cell phone to improve battery life (ie. if you have a laptop handy, use it!)
* Use a darker wallpaper
* Vibration takes up more battery than ringtones
* use a simple theme
* Dont keep your cell phone charging for long periods (eg. overnight)
* If you plan to buy a new battery, buy a branded authentic one
Hope this helped, thanks for using FixYa!

Heat can degrade performance of your iPhone's battery. So it is important to keep the iPhone out of the sun or a hot car (including the glove box).

• Set auto-Lock interval (Settings > General > Auto-Lock) so that your iPhone will turn off more quickly after a period of inactivity.
  

• Apple has also provided some tips to optimize your iPhone settings to extend battery life:
  

  • Use location services only when needed (Settings > General > Location Services).
    

  • Turn off push notifications (Settings > Notifications)
    

  • Fetch email or other data less frequently (Settings > Mail, Contacts, Calendars > Fetch New Data).
    

  • Turn off push mail such when you don't need it (Go to Settings > Mail, Contacts, Calendars > Fetch New Data and set Push to Off).
    

  • If you rarely use Wi-Fi or in a area where there is no Wi-Fi coverage then turn it off (Settings > Wi-Fi).
    

  • If you hardly use Bluetooth then turn off Bluetooth to save power (Settings > General > Bluetooth)
    

  • Turn on Auto-Brightness to allow the screen to adjust its brightness based on current lighting conditions.
    

  • Dimming the screen will also help in extending battery life.
    

  • If you're on the plane or in an area where there is no coverage then use Airplane mode to increase battery life (Settings > Airplane Mode).
    

  • Turn off equalizer setting to song playback as it can decrease battery life (Settings > iPod > EQ).
    

  • As you might have noticed, you can use the iPhone for a longer time to surf the internet on 2G (up to 12 hours) as compare to on 3G (up to 5 hours). So you can turn off 3G to extend battery life (Settings > General > Network and set Enable 3G to Off).
    

  • You can improve battery life by minimizing the use of iPhone apps like games as they prevent the screen from dimming and iPhone apps that use location services.
    

  • Apple advices users to update their iPhone with the latest iPhone OS.
    

  • You should also use the iPhone regularly for proper maintenance of a lithium-based battery. In fact, Apple advices users to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down).
    

  The tips are useful especially when you're travelling and need battery life on your iPhone or iPod Touch for a longer time, or when you're running extremely low on battery and want to save power as much as possible for something important.
  

  I hope you find these tips useful. If you have a tip that you want to share then feel free to tell us in the comments.