The Android 4.1.2 update includes Project Butter, which makes the phone free from lags, and Google Now pushes out cards with information you need, when you need it. Actionable notifications allow you to return calls, view pictures and video directly from the notifications shade. Also being added to the phone is Voice Search, which allows Google to offer some Siri-esque capabilities. And the Smart Keyboard has a more accurate dictionary allowing the keyboard to guess the next word before you type it.
The update will be sent out OTA and it will take 10 to 15 minutes to download and 5 to 10 minutes to install. During the latter process, you will not be able to make or receive any calls. You can also try to manually coax the update out of your phone by manually checking for it. To do this, go to the Home Screen and tap Settings > About Phones > Systems Update > Download.
source: Verizon (1), (2) via AndroidGuys