1* The simplest way to enable USB Debugging. Download ADB Toggle from Google Play.
2* The other way;
For Android 2.x
1. Launch the Settings on your android devices.Tap Application
2. Tap Development and Check the box for USB Debugging
For Android 4.x
1. Launch the Settings on your Android devices.Tap Developer options
2. Toggle the USB Debugging option.
Note: On Android 4.2 + newer and custom roms Developer options is hidden by default. To make it available, go to Settings > About phone and tap Build number seven times. Return to the previous screen to find Developer options.
ENJOY
CULLED FROM ADB DRIVERS
