Let's start with some less dangerous things to try...
- Disable automatic brightness and turn down brightness as much as it fits your eyes
- Disable (some?) window animations
- Disable auto-rotating screen
- Shorten time until your phone goes into sleep mode
- Turn on flight mode as possible
- Tip: Use an app for that. For example, I'm using an app called Smart Phone which automatically changes various settings depending on conditions like location and time.
- Some widgets are drinking your battery juice like water...
- There is a list of programs currently running available in the settings. Take a look at this list in different situations and note which apps are running all the time. However, please keep in mind that some applications don't work properly without constant background operations (for example Announcify ;)). Try to find a balance between less apps and functionality.
The following isn't dangerous at all, but could temporarily break some of the "smarts" of your smartphone, like instant mail- / facebook- / whatever-notifications:
- JuiceDefender. Set it to disable Wifi, and if you don't need instant mail notifications tell it to disable mobile data too.
Now let's get dangerous...
- If you don't have the pure Google Experience (Nexus * phones) you're very likely to have crapware installed, draining your battery even faster. Most of them are useless anyway, so let's remove them:
- If you are running Ice Cream Sandwich, skip to step 4.
- Root your phone. If you don't know how to do that, google it.