If you can't get a signal, turn on Airplane Mode by swiping down and tapping the Settings wheel.
On Android 7, here you can also see how much “Cell standby” or “Mobile standby” is eating up – this is the amount of power your phone gobbles up while not being used.
The stupid web browser still crashes all the time and I hate how they removed the user agent option so now mobile sites load all the time.
Sure you can click the new “request desktop site” button but you have to do it every damn time because it doesn’t remember.
If you don't need a permanent window into Twitter, or regular updates on the weather, remove the superfluous widget by pressing and holding it, then dragging it to the trash can icon.
Smartphones use more power when trying to connect in low-signal areas.