The surgeon general of Iceland has published a sensible COVID-19 primer for people who seem to have more risk of getting it worse.

• Risk increases with age, especially after 50
• Individual with underlying health issues like high blood pressure, cardio-vascular issues, diabetes, pulmonary edema, kidney issues and cancer are in danger of getting sicker than others if they get COVID-19. It is currently not known how much more likely that is, and it is also clear that if the underlying condition is mild or managed the risk factor drops again.
• Smokers seem more at risk, but that may be due to an underlying (possibly undiagnosed) pulminary condition brought on by long-term smoking.
• It is not clear at this point whether immunosuppressing therapies like steroids, methorexate or some bio-tech medicines increase the likelyhood of a serious case of COVID-19.

The disease spreads via touch or droplets. That means the virus can spread when an infected person coughs, sneezes or touches their nose and then a healthy person gets drops or droplets in their face - or their hands touch droplets and then touch their face.

It is worth pointing out that people with underlying conditions are not likelier to catch this in the first place, even if they are likelier to be worse off if they do. So there are no special tips on how to avoid this, just the general rules of avoiding transmission when interacting with other people, especially outside the home.

Limiting contact with other people is the single most important thing to do!

Other people in the household need to take this into consideration too and follow the basic hygiene guidelines and if they may have been exposed at work or elsewhere to limit their contact with the compromised person. If there are many people in the household who are going about their business daily, the compromised person might be better off finding accomodation where contact is more limited. It is also very important to limit contact with children who frequent schools or day care as these are know cesspools at the best of times.

• Wash your hands! Use water and soap and sing the 20s chorus of a popular song (to yourself or to others depending on your mood) to make sure you do it thoroughly. If hands aren't dirty but you touched some communal things like elevator buttons, handrails and such, hand sanitizer will do just fine.
• Use disinfectant wipes to clean off things like handrails, shopping cart handles and such before touching them. This is also a good general rule when traveling on aircraft.
• Avoid people who have general symptoms of a cold; coughing, sneezing or sniveling. If you're in an area where contagion is widespread, stay home as much as you can - even if the general population is not told to isolate.
• Masks are of most use for individuals who are sick, but can be appropriate for those who are compromised when likely to come into contact with sick people, like in health-care waiting rooms or at the doctor's.
• Avoid cleaning up after others, especially outside the home. If you can't get someone else to do so, use disposable gloves and get rid of them immediately afterwards and wash your hands thoroughly.

• Stay home as much as possible and limit the number of people you interact with directly.
• If you need to seek medical attention, show up on time and do not spend more time than absolutely necessary in the waiting room. Wear a mask and keep your hands to yourself - and clean them regularly.
• Regular preventive appointments like dentists and non-essential health-care or personal maintenance should be canceled.
• Do not use public transport. You're better off being driven in a private car - or a Lyft, Uber or Taxi which are easier to wipe down. Again, keep your hands to yourself and keep them clean.
• Don't go to work or school if that means you'll come into contact with many individuals. If you work in a small office - or have space to yourself - you're probably safe if you follow the general guidelines stringently, but consult your employer or school.
• Don't go to public or semi-public events, even if they're not canceled. This also means parties, birthdays, funerals, concerts etc.
• Likewise, don't go to the gym (yay!), church, the pool, theatre or movies - or the mall - or wherever people congregate.
• Don't go to places where many people visit over the course of the day, even though few people are there at a time. This includes salons and such where the employees are in close contact with multiple individuals regularly.
• You're off the hook for running errands as well. Send someone else to the store, or to pick up food, the mail, go to the bank etc. Some of these places might need a note from you to allow someone else to pick up your stuff, especially pharmacies and banks. Use delivery services or drive-throughs.
• If you can't avoid going out and about your business, bring your own shopping bag, use disposable gloves and disinfectant wipes on shopping carts. Avoid touching things as much as possible.
• Stay out of common areas and don't loiter in lobbies, stairwells etc.
• Avoid visits and visitations as much as possible.
• Keep sane. Get out, go for walks (keeping your distance from other people), stop and smell the flowers (if available). Do regular exercise at home, there are plenty of YouTube videos to help you get a work-out at any level. Use streaming services to get access to quality entertainment and do not get stuck watching the news where everything seems to be going to hell. It's not - you'll be fine.
• Remember to wash your hands after taking out the trash or picking up the mail.