Clear all used apps before charging and/or put the phone in airplane mode if possible. That way you'll get "rapid charging" (around 2 hrs and 40 mins, from 0 - to 100%).
For battery mileage, make sure as many apps as possible are battery optimized, especially Android System. Turn off it's background activity ("Apps background is limited when not in use"). Also deny background data usage for apps for which you think background data access is unnecessary. The same goes for access to location services.
Allow auto-sync only for important apps like Gmail and Contacts and possibly your other chosen apps. Keep Data Saver turned on. Disable wifi scanning if not necessary.
Uninstall or disable any apps that are useless to you via the conventional method or via adb, if necessary (I safely uninstalled/disabled a total of 23 system apps and a few more 3rd party bloatware ones).
Cut down Window and Transition animation scales and Animator duration scale to .5x in Developer Options. This will speed up operation of your phone and overall power wastage on animations will be reduced. Keep notifications on only for the apps/system apps that you need.
Read somewhere that by running the battery down to shut off and recharging it to 100% in off mode before restarting it in fully charged state - before unplugging it, will "calibrate" your battery. Dunno how far that is true but I've done it the prescribed 3 times - just in case.
Wipe the cache partition via recovery mode after a big ass, major update.
Use Naptime like me!

I have never cleared my cache partition since day one. Haven't had any battery drain issue. Hmm...maybe I should do it since charging my phone takes like 4 hours now to 100%.