Settings, apps, running, and see what's running. Install wake lock detector and greenify. Let wake lock run a while and greenify the bad apps. You can also go into app permissions and deny a good many wakeups but you have to pick and choose cause you can prevent the app from working.
Also choose a governor other than interactive, like on demand and noop or sio for scheduler.
Also turn off WiFi and anything else if your not using it, location especially.
HTC One M8 powered by SinLess Audiophile v3.5.5/Elite Lunar 3.4.0