I wanted to use Cyanogen Mod on my Verizon Nexus so I first needed to root my phone so I used the Galaxy Nexus ToolKit you can read my previous post about how to use the toolkit [HERE]

I selected my current Rom which at the time was ICS 4.0.2

Then I made my selection to unlock my bootloader, Root my Phone, and other options by pressing option 7

Then after it was done rooting, I went to the Google Play store and downloaded Rom Manager by ClockworkMod

1. Install  Titanium Backup. Run Titanium Backup and save all of your apps and data.
2. Download the ROM installation ZIP for your phone and place it onto your SD Card.
3. Reboot your phone to Recovery mode, scroll down to “backup and restore”, go in, and select the “Backup” option. This will write an image of your phone onto your SD Card. OS, your apps and settings will be saved.
4. Perform a full wipe of your device from Recovery by doing a “wipe data/factory reset”, “wipe cache partition”, and “advanced -> Wipe Dalvik Cache”.
5. Select “install zip from card” option, and then “choose zip from sdcard” to flash the ROM zip that you downloaded in step 2.
6. Optionally, flash the GApps package, and any other files (refer to the ROM’s instructions.)
7. Once the installation is completed reboot the phone, add your Google account, and set up the system to your lining (do not download any 3rd-party apps yet.)
8. Open the Market app, install AppBrain and Fast Web Installer again, and sign in.
9. Open the Appbrain app, and enable Fast Web Installer in settings again.
10. While still inside the Appbrain app, go to “Manage And Sync”, press the Menu button, select the “More lists..” option. Pick the list that was created for you in step 1, and press the “Add all apps” button. This will queue up all the missing apps that you had installed on the previous ROM.
11. Go back once, and tap the “Execute” button. After verifying the permissions, tap the Install button. This will automatically download and re-install your apps.
12. Once the apps are installed, configure them to your liking.
13. Reboot back into Recovery, perform another backup, and reboot the phone normally.
14. Open the ROM Manager app, and tap on “Manage and Restore Backups.” You should see a list consisting of the 2 backups you just made, sorted chronologically.