When it comes to charging your iPhone (or any mobile device, really), it's a simple process: plug it in. Well, believe it or not, there is one thing you can do to significantly speed up the charging process.
When you switch your phone into "Airplane Mode", it turns off all radios (Bluetooth, WiFi, cellular, etc). These radios use a significant amount of power, and when these radios are active while charging your phone, they're actually using some of the power that could be charging your battery.
To speed up the charging process, simply put your phone into "Airplane Mode" and dim the screen. This will ensure that nearly 100% of the power coming from the wall charger is going directly to charge your battery.