Battery advice circulates widely and much of it addresses things that consume almost nothing. These are the settings that matter.
The screen
By a wide margin the largest consumer. Brightness is the single most effective setting, and automatic brightness tends to run higher than necessary indoors.
Screen timeout, set shorter. And dark mode on an OLED display, which genuinely saves power because black pixels are switched off – though not on LCD, where it saves nothing.
High refresh rate costs battery. Setting it to adaptive or a lower fixed rate makes a measurable difference.
Location
The second largest, and the easiest to fix. Set apps to use location only while in use rather than always. Most phones show which apps requested location recently, and the list usually includes several with no reason to.
Background activity
Apps refreshing content when you are not using them. Both platforms let you restrict this per app, and restricting everything except messaging and email costs nothing you will notice.
What does not help
Closing apps from the multitasking view. On both platforms this can increase consumption, because relaunching an app from cold costs more than leaving it suspended.
Battery cleaning apps, which consume power to tell you about power.
Where the drain is hiding
Check the battery usage screen. It lists which apps consumed what, and the answer is frequently one specific app behaving badly rather than general use.
Poor signal is the other hidden cost. A phone searching for a weak network uses far more power than one with good reception, which is why battery drains fast in rural areas and basements.