What usually consumes more energy is brightness and graphics. So:
- avoid effects, unless they really bring some experience improvement
- avoid plasmoids
- reduce brightness to a level in which you can still work when on battery
- disable the boost clock and limit cpu clock to a fair maximum (depending on your needs)
- usually, you can also limit the gpu clock
Many of these settings can be configured in TLP. Others require udev rules, for example, and others can be configured in KDE energy settings. There are also other options related to WiFi and disk activity which can be configured in TLP.
I can paste my laptop config later (I’m on my desktop now). I have my cpu and gpu clocks limited there, and it improved a lot my battery time. Of course I don’t use that machine for gaming. I mostly don’t miss the extra power when working (except when I need to do some image editing - processing is noticeably slower).