Prevent problems before they even happen
The overall aim of upstream work is to prevent problems before they even happen. Instead of constantly putting out fires, you should work towards not having any fires in the first place!
Identify a costly problem that can be prevented.
Take the simple example of house maintenance - often, electronics like airconditioners break because they have not been serviced regularly. Fixing them is much more expensive than regular maintenance!
Identify who is in the best position to prevent this problem
Often, you may not be able to directly do anything to prevent a problem. What you can do, however, is reach out to those who can prevent the problem.
Create incentives for them to prevent the problem
For example, if you want to reduce the burden on the healthcare system, one way is to prevent patients from getting sick so often. You can do this by creating incentives (financial, for example) for doctors to treat their patients more effectively.