If you spot patterns within the categories, note how many different kinds of errors there are within the category. You may find as many as five or six sub-categories of error within some of the more inclusive, larger categories like sentence-punctuation errors.
Note an example that illustrates each of the sub-categories you think you want to take up with the student.
Rank the sub-categories in some order, most likely how you can use one explanation to build up for a second sub-category. For example, if the writer uses all connecting words in the same way, you will probably need to start by explaining the different kinds of connectives in English sentences. Then you can build--eventually--to your explanation of when to use semicolons with certain kinds of connecting words.