If you have a poor mobile phone signal, your phone's battery will drain quickly because the phone is constantly looking for a stronger signal. It could be your worst offender. If this is the case and you have a good WiFi signal in your house, you'd be better off using voice over WiFi at home.
As others suggest, having lots of running apps in the background does not help so close them all when you are not actively using them.
Keep Bluetooth turned off unless you need it and turn on WiFi only when you trust it (in your home or at a friends' or relatives' house). Moving around with these switched on causes the phone to scan for networks, it's also a security risk. (They can also scan when switched off - hidden in 'Advanced' settings.)
Using mobile data can also drain a battery quickly, (downloading videos) especially in an area where there is a poor signal.
Location services also use battery power and you can reduce the frequency that your email client downloads your mails.
www.cultofmac.com/238746/fetch-or-push-set-your-email-accounts-to-maximize-battery-life-speed-of-delivery-ios-tips/
Some apps, can also drain the battery, especially if they require intensive use of the graphics card. You can identify any power hungry apps:-
www.howtogeek.com/197074/how-to-see-which-apps-are-draining-your-battery-on-an-iphone-or-ipad/
I turn off as much as I can (on my Android phone), then turn on what I need as required. I do this to save my battery and to keep my phone more secure too.
It doesn't take long to toggle WiFi, location settings, Bluetooth and mobile data on and off.