What's the worst habit a student can develop? They grab their pen and filling the page with ideas as they think of them. Your grammar and style might be great, but you'll turn in a weak essay. Train yourself to analyze questions and decide your main points before you write. The best writers in the world do this. There's no reason you should not.

Teachers struggle to convince students to form brainstorming and planning habits. These have a noticeable effect on your output, so make them a routine step of your writing process. You'll be able to plan your time better, and you'll enjoy writing too.