Install
1.Use CWM5.
For flashing with Odin: recovery-clockwork-5.5.0.4-ariesve.tar.md5
For manually flashing: recovery-clockwork-5.5.0.4-ariesve.zip
•Warning: Only use this recovery to flash CM9. Otherwise, you risk bricking your phone!
2.Wipe data and cache.
3.Flash update*.zip.
4.Flash gapps*.zip. You must flash gapps after every upgrade to CM9 since /system is formatted, wiping your previous add-ons.
5.Reboot phone.
6.After you setup your Google account, reinstall the three apps from Market in order to restore most of your apps, call log and SMS history.
7.Warning: Do not restore backup data of system apps!
•If you restore a bad backup with cached settings in telephony.db in data/data/com.*.*.telephony it can break MMS.
•It seems that restoring backups can also break Calendar sync.
Upgrades
Upgrades from previous versions of CM9 are the same process as install, except you do not need to wipe anything. Contrary to popular belief, you do not need to even wipe cache and dalvik-cache when upgrading between CM9 versions. You only need to wipe if you are doing a major upgrade, switching to a different ROM entirely, or attempting to fix bugs caused by bad backups or corrupt app data.
for people still having problems reading first page !!!