- Turn off all unnecessary connections. That includes GPS, NFC, Locationservices, Sync, etc. That alone will save you days.
- Turn off WiFi when you're not using it.
- Greenify all apps before you turn the screen off. Android keeps apps running in the background for quick access, but it eats battery. Yes, greenifying them will mean they take a second longer to open, but it'll save battery life.
- Turn down the brightness. Use LUX to go below 0%. (Which doesn't actually mean the screen turns off.)
- Disable or delete all bloatware, or as much as you can.
- Using a MicroSD? Drop a .nomedia file in every folder that doesn't need to show up in a mediaplayer. (pdf's, comics, etc). You can still open the files through a filemanager, but MediaScanner/Indexingservice won't freeze on them.
- Turn off all unnecessary sensors. Especially if you're using a Samsung, those have quite a lot of sensors.