If i get coronavirus, are there ways to avoid getting other illnesses as well, like pneumonia?

Corona: The isolation guidelines are good for all sorts of illnesses. Your are older than 70 so your concern about the virus is justified. However, if you do not have a lot of co-morbid conditions your risk of sever illness is low.

Coronavirus: COVID-19 has high affinity to the lung, causing viral pneumonia. Fortunately, most people get only mild respiratory symptoms. Those who have high risks (age over 65, chronic diseases) tend to get pneumonia and complications. The most important way to prevent the complications is not to get infection, practice common sense of prevention. If you catch the infection, start early treatment.