Show students examples of bad grammar and poor proofreading. Often, it is important for students to know what the world would look like without proper grammar or proofreading. Improper grammar is something we notice when it is done incorrectly, but most of the time, because editors fix mistakes before they go to print, we don't see the errors. Find examples of signs, newspaper headings or articles with poor proofreading, and ask students to evaluate them. The first step in motivating students to proofread their work is to show them what a finished product could look like without an editor's expertise. Ask them what opinions the world would have of a newspaper or novel with poor proofreading.
Show student examples of papers at different levels. Students are most of the time much harder on their peers than teachers are on students. Ask students to proofread an anonymous paper with lots of mistakes. Then, ask them to read through a paper with few to no mistakes. Ask them which was easier to read and understand and why. Ask them which deserves the better grade. Sometimes, when students see another student performing poorly, the competitive edge kicks in, and they will be motivated to do better than what has been done before. Set the standard for excellence, and excellence is what you will receive.
Do editing practice warm-ups each day and offer grade points for successfully completing them the first time. Editing practice warm-ups allow students to hone their proofreading skills quickly and relatively painlessly. The examples you choose should only have 10 or fewer mistakes. Give students 10 to 15 minutes at the beginning of class to proofread them. Ask students to exchange papers. Review the corrections made as a whole class with students marking any missed errors on the paper in front of them in a different color. Collect the warm-ups and give a passing grade to those students who found all the errors. You might alternatively choose to give a passing grade to everyone and extra credit to those who found all errors the first time.
Create a paper assignment with a rubric that rewards those who proofread final copies before turning them in. Include wording on your rubric that awards maximum points to those whose final copies have fewer than three errors per page or, no errors at all. This tactic will work for students motivated by grades. Those who are intrinsically motivated to be better writers will want to turn in a final paper that is spotless. For the rest, offer credit for evidence of a rough draft with proofreading marks showing it was read and edited carefully. This way, all students have the opportunity to benefit from proofreading practice and the opportunity to hone these skills at a pace that works best for them.