Battery drain usually comes from a combination of a bright display, poor signal, video, navigation and background activity.
Display
High brightness and long screen-on time are major power users. Auto-brightness and a shorter timeout can make a visible difference.
Weak cellular signal
In poor coverage, the phone uses more power trying to maintain a connection, especially while traveling or inside difficult buildings.
Camera, video and games
Video recording, image processing and heavy graphics stress the processor, display and sometimes the network at the same time.
Location and background refresh
Real-time navigation needs location access, but many apps do not need it constantly. Review which apps can use location in the background.
Bottom line
Keep the solution simple: start with the most likely cause, change one factor at a time, and observe the result. That makes it much easier to identify what actually works in your situation.