Think of a problem that you want solved on your computer or some task that you have to frequently do on your computer. Once you have identified something, start breaking that problem/task into as many steps as you can think of then start writing Go code to solve/perform each of those steps.

Alternatively, you can search for open source applications that use Go as their primary language and check to see if there are any open (and ideally easy) issues that you can help with. Even writing/updating documentation could help you learn Go as you would likely need to reference or be familiar with the codebase to write the documentation.