I never did anything specific to lower mine as they were always low. I'd say it depends on:
- Finding ideal mask (nasal / mouth / full face)
- Ensuring a tight fit (your machine can usually tell you this) - moving around through the night will naturally loosen your mask so once a week undo the Velcro and refit it
Also keep in mind that if you get a sinus infection, cold, something similar that impacts breathing, that will throw off you numbers and you may even need to address the pressure to compensate. The best way to know your pressure is correct is it shouldn't feel like there's anything there when you're breathing, you shouldn't feel the air coming in out or out, it should be effortless.