Some tips and tricks to get the most out of your device

Battery life

If you haven’t yet, install a new battery!
If you have an S6, install an S7/S7 Edge battery in your phone. Check here for more details. You can go from a 2600mAh battery to 3600mAh!
Lower your screen brightness
Disable the hardware navigation lights or use on-screen navigation
Use a wakelock blocker to stop unneeded wakelocks from GMS. (be careful with this one)
Run without GApps - Play Store/Services are very heavy these days. MicroG is a good alternative.
Use AMOLED dark mode
Configure battery saver mode to turn on, which limits maximum CPU and GPU clocks.
Use an adblocker when possible (ie Brave, AdAway root)
Use 2G/3G instead of 4G radios when possible
Limit your charge to 80% to prolong your long-term battery health when possible
Disable Fast Charging and don’t use Wireless Chargers. This can reduce your long-term battery health
Undervolt your CPU and GPU, this can increase battery life

Install a 3rd party camera app, like GCam Go or OpenCamera (these are better)
Use PlayIntegrityFix to get some apps working. Refer to XDA for advice.
Install AOSP mods to tweak the way the UI looks
Use cloud storage to maximize your phones local storage
When setting up fingerprints, instead of setting up 2 seperate profiles for 2 fingers, use 1 profile for 2 fingers (50% for one, 50% for another). This is faster than having to setup 2 different profiles
Install my TWRP for OTA updates
Change your resolution to 1080p or 720p to get better performance in games.
Undervolt your device, this can reduce heat output

Keep your ROM and Play services updated
Use SELinux Enforcing where possible
Avoid outdated Android 5, 6, 7, etc ROMs
Install trusted apps and mods only to avoid malware. Using Aurora Store and F-Droid is generally safe

Create backups of your device sometimes - just in case your NAND dies
Use a case and screen protector - this is super cheap these days and can protect your device
Don’t pull on USB cables. The port is directly soldered to the board, so is hard to replace.
Keep your phone cool to reduce the chance of it un-aliving itself