Again, the main focus of the Vocabulary Paper is not the vocabulary words, but the mechanics and the student’s accountability for correctness in those mechanics. You might not go any further with the “Style Book” than those errors covered by the vocabulary paper correction sheet. With some classes, however, you may want to add to the list to cover such issues as punctuation, agreement, parallel structure, pronoun case and reference, dangling modifiers, shift in tense, and the like.
My experience has been that the most common abuses of these are subject-verb agreement, pronoun case, shift in tense, and punctuation, especially the comma.
On the assumption, then, that the most common errors ought to be dealt with first and longest, the logical first additions to the Style Book ought to be about agreement and tense shift, but I find that comma usage is a better beginning because, while it is not as egregious an error, it’s very common and it reinforces what has already been shown about clauses and phrases, especially as logical constructs.
(Another caveat: It would be a mistake to simply give the class a handout listing the Style book “rules” about editing and the solutions to correcting mechanical errors. That would tend to absolve the student of one level of responsibility for the knowledge. Not that the student will learn those “rules” just by writing them down, but writing them himself becomes one step in what is necessarily a repetition of steps before he’s likely to assimilate the knowledge.)