As Samad Bhai (Sam_vitz007) says:
Stick to static wallpaper,
Apply a screen friendly wallpaper,
Uncheck vibrate when typing,
Remove all kinds of vibration,
Use Advanced Task Killer by Rechild to kill all background programs,
Set screen brightness to 50% (Screen is the major cause of battery in Xperia series),
Dont put Calender widget on any of your homescreens.