First, you want to install Bootstrap or Safestrap for backing up and restoring roms.
For starters, use Safestrap.. Download the
Safestrap 1.06 apk.
Put that APK on your phone and install the recovery but make sure you don't have bootstrap installed already.
Once you install safestrap:
1) Power off your phone.
2) Power on and you will see the Safestrap Splash Screen after the "Dual Core" screen goes away --> PRESS THE MENU BUTTON. You will have 10 seconds.
3) From the CWR, go down to backup and restore, and select backup. (Use Volume up and down to navigate and power button to select)
Backup to either External or Internal card.
Once it is complete, stay in CWR and
wipe data/factory reset,
wipe cache (For good measure), and
format system (Under mounts and storage)
After you finished that,
Install CM9-Droid 3 and thats it!