First of all:
Let phone drain battery completely until it’s off ( do this once a month )
Charge before it reaches 20%
Unplug at 80%
Turn off Background App Refresh
Turn off Auto Brightness in Display settings and Accessibility
Turn Off Siri Suggestions
Privacy - Location Off
Keep your brightness very low
Make sure Bluetooth and Mobile data are off
Turn off Exposure Notifications
Just make sure you’re charging your battery properly. You don’t really have to charge it to 100% during the day, you can do that overnight. And you could turn off optimised battery charging of you want to.
Hope this helps!