Simplified a little for nexus 7
This sideload guide is for stock recovery.
If you are using TWRP, copy the update.zip to your virtual sdcard, then boot to recovery, choose Install, select the OTA update.zip file, then swipe to install.
Simple guide to adb sideload:
- adb reboot recovery
Alternatively, power down tablet and press/hold Power+VolUp until you see Google
You'll see fallen down android, press/hold Power, then press/release VolUp, then release Power, you will then see Recovery menu- Select "Apply update from ADB" using VolDown
Press Power to select- adb sideload update.zip
Suggest renaming long OTA update filename to update.zip for convenience- update should begin loading
If you have trouble with an unknown device named Flo, see this post for adb drivers that will work in recovery:
http://xdaforums.com/showthread.php?t=2391236
I have TWRP and did as you said but update still fails.