I read their essay and I make a dot at the end of each line that contains a grammatical mistake (spelling, punctuation, usage). I will circle tired or overused words and demand improved vocabulary. That's about all I have time for with over 100 essays to read and review
I hope that helps you. I also recommend writing essays in stages. I always begin with body paragraphs; grade and return. Then, I move into the introduction and conclusion. I have my students type the finished copy, mark the body paragraphs, and I only have to review the introduction and conclusion.
When I ask my students to mark the body paragraphs they must:
bold the topic sentence,
highlight their eveidence or examples in each paragraph, and
underline the transititions. The only part of their paragraphs that is not marked is their explanations or linking information.