2. What should be done refers to the general state and should be done all the time; What should be done is a state of progress, something that should be done at a certain time or moment. Here, promote health. If you are healthy, you don't need to promote it. It is also something that needs to be done in a specific state. You don't have to drill that deep. In fact, generally speaking, you can use should do, which native speakers may not think of.