There is so much advice floating round in cyberspace right now on virus prevention and immunity. My own advice is fairly simple:
Eat a balanced diet - maybe cut meat consumption to 1 meal a day, or even every other day. Eat more plant based food, and a variety.
Exercise - during lock down that might be limited to walking, or home based options such as yoga, tai chi, treadmill and so on. Staying fit builds immunity and helps our tolerance to everyday stress.
Try and get some sun on our skin each day...