Set power management to power saver mode in advanced settings.
Lower monitor's brightness.
Make sure your bios settings using S3 to S5 suspend. Power settings there too, like fan speed.
Underclock or unvolt since no plans to play games or other heavy work.
Check if your GPU actually lowers its performance. E.g GPU clock around 800mhz instead of 1600+ mhz while doing light load stuff like watching videos. If not, check GPU settings.