What is the best covid-19 prevention advice for people who are older than 50?

Same as for younger: Wash hands (or use sanitizer) often for at least 20 seconds. Wash hands before touching eyes, nose or mouth. Use a cloth cover over mouth & nose when around others. Stay home as much as possible. Avoid sick people. Distance at least 6 feet from others. Clean/ disinfect frequently used surfaces. Stay hydrated. Get a good night's sleep. Eat healthfully. Get your flu and pneumonia shots.