First, turn off Auto-Sync in the Settings>Accounts & Sync menu.
My advice would be to root the phone.
Then download Titanium Backup and FREEZE both of the Wi-Fi Sharing processes.
Also, in Titanium Backup, backup and then Un-Install AP News and Accu Weather (if you have those factory installed.)
Also, avoid data heavy widgets.
Keeping the screen brightness to 1/3 and Auto is about right in most situations.
If I don't use my phone all day, the power level barely drops. If I am playing games, checking facebook, browsing the web, texting and calling all day, I only get about 6-8 hours out of it before it's asking to be fed.