Install Problems
If the app does not launch, verify that the download came from the official release page and recheck any OS security prompt you dismissed during first launch.
Connection Problems
Separate network, authentication, SSL or SSH, and schema issues. Solve one layer at a time instead of changing multiple settings blindly.
Query Problems
When a query behaves unexpectedly, simplify it. Remove joins, reduce selected columns, and add LIMIT until the failing assumption becomes obvious.
For narrower problem classes, continue with Install & Launch Issues, Connection Failures, and Query Debugging.