I look at the error message and the Traceback if there is one, then i go to the code line in question. If there is no Exception and there is som kind of logic

I look at the error message and the Traceback if there is one, then i go to the code line in question. If there is no Exception and there is som kind of logic bug. I search my way to the logic code with the issue by greping and reading. When i have found the approximate location of the issue i will probably set up some var_dump's or log.Println in the code to get a better understanding of what is happening. After that it is usually a done deal.