It has been a number of days since I made a number of changes to try to increase the battery life of the MIUI 2.6.1 (Android 4) installation on my 1.5 year old HTC Evo 4G. And presently I'm pretty happy with my battery life, as it is very close to the life I was getting with Cyanogen 7 + Go Launcher.
I'm easily getting a good full day of occasional use throughout the day. Also it should be noted that I leave the Wifi antenna on all the time.
In Menu -> Settings:
* Display -> Brightness -> turn off automatic brightness, set to about 1/3 on the slider
* Display -> Launcher -> turn off Icon shadow
* Display -> turn off Auto-rotate screen
* Display -> Sleep -> set to 30 seconds
* Accounts & sync: everything off except my Google account, and only syncing Calendar, Contacts, and Gmail automatically.
* Developer options -> on both 'Window animation scale' and 'Transition animation scale' turn animation off
Under the MIUI folder launch the 'MIUI.us Toolbox':
* CPU Settings -> CPU Governor to 'conservative', min = ~250MHz, max = ~1000MHz, restore on boot = ON
* MIUI Launcher Settings -> uncheck Allow Rotation
With these settings in place, I've been pretty happy with MIUI. The only change that I'd make is change out the default browser with Dolphin Mini (or Dolphin HD if you want a bunch of the addons).
Hope this helps! Cheers!