Android L Release: Developer Preview Build Installation - Kapil Sharma

Steps for installation of Android L on Nexus 5 and Nexus 7 series devices: 

Step 1: First download the relevant Android L OS file from Google site. (http://developer.android.com/preview/setup-sdk.html)

Step 2: Than open developer options on your Nexus device. These options are hidden. 
So go to Settings > About device and then tap on the build number 7 times. 
Once you have done that, you will find developer options in your Settings menu.

Step 3: Open developer options and make sure USB Debugging is ticked.

Step 4: Check if your computer has the relevant drivers required for Nexus devices. 
If not, download the drivers from here and install. 
(http://developer.android.com/sdk/win-usb.html)

Step 5: Make sure you have ADB and Fastboot Installed. For this, follow the steps from here (http://forum.xda-developers.com/showthread.php?t=2317790)

Step 6: Connect your device to computer and open ADB (it will open in a command window). Type adb reboot bootloader. Your phone will go into recovery mode. 
Check the screen and see that for Bootloader status it shows unlocked.

Step 7: Most likely your device will have the locked bootloader. 
To unlock it, type fastboot oem unlock. Then follow instructions on your phone screen. 
This will unlock bootloader as well as do a factory reset of the device.

Step 8: Disconnect and reconnect your device to PC. 
You may have to go into settings again, reveal developer options and select USB debugging.

Step 9: Unzip the Android L file you had downloaded. Create a new folder with an easy to type name like Android and put all the files in it. Then put this folder into Minimal ADB and Fastboot Folder which is in your computer's program folder.

Step 10: Hold SHIFT key and right click on the Minimal ADB and Fastboot folder. 
From the menu, select "Open Command Window here".

Step 11: With your device connected, type adb reboot bootloader.

Step 12: Navigate (use CD to change directories) to the folder where Android L files are stored.

Step 13: Type flash-all in the command window.

Step 14: If you have done everything right, Android L will be installed on your device. 
It will take up to max 15 minutes though. 

Warning: This is an developer preview build this may contain bugs and leads to device crashes.