Come up with an end-note formula that works for you, i.e., open with a positive statement, point out one or two major problems, then close with a "where to go from here" comment. This formula will help you save time and achieve consistency from student to student.
Post a list of what you are planning to comment on in any given essay assignment. As much as possible (excluding glaring problems that need to be addressed), stick only to the criteria on the list.
Set a time limit for each essay. Again, excluding serious problems, try to at least average out on target for your time frame.
Don't rewrite student sentences to give them "examples" of how to be more descriptive, concise, etc. It takes too much time and they hand in revisions with your comments taken like Bible (and too often the rest remains the same).
Don't let awkward sentences, grammatical and mechanical errors, etc., become too distracting--look for major strengths and weaknesses.