Not using an electric toothbrush. First time I used one it felt like I'd had a proper dental cleaning. An extremely half-assed effort with that kind of brush beats a thorough one with a manual brush. I thought they were a gimmick, but no, they're amazing.
I destroyed my gums when my parents got me an electric toothbrush when I was 13 - and AFAIK - there's still not really any way to repair it.
Please, someone correct me if I'm wrong! Would make my day to be wrong.