Helpful strategies

Take the time to get familiar with each table in the ERD. Run basic queries to understand the tables and how they relate to each other. This is a critical foundational step to building advanced queries.
Start creating and posing your questions, then work backwards to identify the tables you'll need to answer your questions.
Pay attention to the intermediate query results you will need to take to get to the final query result.
Break down the logic of the question to identify and draw out the table for each subquery and the final query result you are aiming for. These intermediate tables can also help you identify any subquery, common table expression or Window Function you may need to run.
Take breaks! Abstract concepts need time to percolate through so you can see a solution. When you find yourself in a rut with a difficult problem, take a short break and then come back to try it again.