A writer should

to organize ideas for a document-based essay.

Create an outline.

Explanation:

'Outlining' is elucidated as the process that aims to offer a map or plan of the entire idea or content that is going to be displayed to the audience.

As per the question, 'creating an outline' would help in organizing an essay that is document-based as it would assist in categorizing the key points of the work along with its sub-points and evidences that would be presented to substantiate each claim in a format. Thus, it helps in proffering an organized form to the content that would establish the coherence in ideas.