>>283049597
Measure your IPD and ensure your headset is adjusted accordingly. Check strap fit and try to equalize tension across all straps. The top one is easy to ignore but if it's loose you're putting too much pressure on your cheeks. Use a microfiber cloth to clean off the lenses every time you put the HMD on. Maybe consider getting one of those cloth facial interfaces from VRCover, since the foam can get abrasive.
Stay hydrated, and set up your playspace so that it's well ventilated and at a comfortable temperature.