The writing stage is often called drafting. When you draft, you should be focused mainly on ideas, rather than worrying too much about your grammar. Use your outline as you draft to make sure you don't lose your focus.
Many students find it easier to begin drafting the body paragraphs before drafting the introduction and conclusion paragraphs. This can be an excellent strategy to write more efficiently because the introduction and conclusion are based off what you write in the body paragraphs.