2. Preserve Battery Life
If you're new to the iPhone (or any smartphone), the first thing you'll notice is that the battery life is dreadfully short. While the iPhone 4 battery is much better than previous iPhone models, it still draws a lot of power and can get really hot. You'll have to charge it every day, and maybe more than that.
Once you become dependent on the iPhone, a dead battery will be like a best friend deserting you in a time of need. You'll no doubt suffer the five stages of grief: denial and isolation (I'm so alone without Facebook); anger (Apple has got to build a better $%&@ battery!); bargaining (if I can just have a little more juice, I promise to stop playing Angry Birds); and, finally, acceptance (I can't live without my precious).
Many tricks help preserve iPhone battery life, but they all come down to a single idea: You must now be mindful about something that you didn't need to worry about before.
First, you should make the percentage of remaining battery life appear next to the battery icon on the upper right corner of the iPhone screen. To do this, tap Settings-->General-->Usage-->Turn on Battery Percentage. A numerical percentage helps you check the battery regularly, as opposed to suddenly being surprised by a red battery icon.
Next, disable power-hungry features such as Wi-Fi, Notifications and Location Services until you're ready to use them. These apps reach out to the 3G radio and consume power.
The LCD is the biggest battery hog, so you will want to manage the brightness. We recommend turning on auto brightness. Go to Settings-->Brightness-->Turn on Auto-Brightness. Don't forget to turn off Auto-Brightness when watching a movie on your iPhone 4, or else the movie will appear dark.
The overall life of your iPhone battery is constantly degrading. Every time you go through a charge cycle on your iPhone, you'll permanently lose anywhere from 30 seconds to a minute of battery capacity. Typically, you'll get 250 to 500 charge cycles before a lithium ion battery has outlived its usefulness. So if your iPhone is near a charger, plug it in so it's not running off the battery.
(A charge cycle covers the entire capacity of the battery. For instance, if you drained a third of the battery and recharged it, and then used two-thirds of the battery the next day and recharged it, this would still be considered a single charge cycle.)