The challenge is to debug an approval process, and for some reason, the process has stopped working or you have been asked to enhance it further. You are a new administrator to the firm, and you have no prior knowledge of what's already built and how to analyze the existing approval flow.
The first step would be to take a print of the approval flow diagram. You will find this on the approval process. The View Diagram button on the approval process will display the flowchart.
Understand the business need for which this process was written. This is important as you will get a sense of the actions written. Go to each of the approval steps and actions, and work on each criteria and action; use the Salesforce debug log to get more information on what's triggering and what's not. An obvious reason could be some logical issue on criteria or actions.