Is it actually the quality criteria they want you to address in more depth, or is it really the depth of the analysis itself that needs more depth? The former (quality of the study) usually becomes quite evident if the latter (depth of analysis) is adequate.
One of the best strategies is to consider what it is in your data that has convinced you of your conclusions (helped greatly by having kept an audit trail as you worked through your results). Then you can structure your argument to support your conclusions according to those considerations.
You will find explanations along with a comprehensive range of specific strategies to help with both aspects (quality of study, depth of analysis) in my book Qualitative data analysis: practical strategies (Sage, 2013).