Galaxy S8 Battery Saving Tips Featuring Package Disabler Pro/IFTTT
Turn off Auto-Brightness
Decrease display resolution
Turn screen timeout to 15 seconds
Use a Dark Theme/Wallpaper/Icon Pack
Use Package Disabler Pro to Disable Samsung Bloat/Unwanted Apps:
Turn off Wifi/NFC/Bluetooth when not in use-IFTTT can be helpful for this.
If you're in a rush just use one of the built in Power Saving Modes to perform several of these simultaneously. These work well, but with much less granular control.