Before getting into debuggers and breakpoints, let's start with some first-response troubleshooting steps. These are the fundamentals. In time, many of them will become second nature to you, if they are not already. In short, these are the things that you need to do at the first sign of even a minor problem, or even just to understand test results in the development cycle.
Good logging remains essential to good software. When things go wrong, one of the first things to do is to check for errors, messages, and warnings that may have been logged in the process of things going wrong. These messages should provide you with at least a starting point for your investigation. Good logging will reduce the scope of investigation and can sometimes tell you exactly what the problem is.
Your own code should also utilize logging to provide appropriate information to users, developers, and system administrators. It should utilize the logging levels so that the levels...