Writing Sample Guidelines

Follow any instructions given; if length is unspecified, between 20 and 25 pages is appropriate.
Make sure the sample is carefully documented, as it would be for publication. You want to show your readers that you are a professional, familiar with the conventions of academic publishing and knowledgeable of current work in your field.
If you have a recently published or forthcoming article, this will often be an ideal sample to send. But it may be more advantageous to choose an extract from your dissertation if your only published option is older or if your dissertation is what you consider to be your best work.
Bear in mind that if you advance to a campus visit and are asked to give a research presentation, it must not be the same as the writing sample. This could influence your choice of writing sample if you have more than good option (for example, if you know that one piece is definitely easier for a reader to digest while another lends itself better to a great oral presentation). However, do not let this possibility cause you to send a sample that isn’t your best work: represent yourself to best advantage at each stage of the process, and cross the next bridge when you get to it.

The writing sample must be in your field/advertised field. Even if you’ve done good work in another field or even had it published, you need to show your work in the field you wish to be hired in.
The writing sample should ideally reflect your major research project/dissertation. But it should not necessarily be extracted from your dissertation as is. This sample must be highly polished and stand on its own. Revise with these factors in mind.
When possible, use continuous pages selected from a chapter.
When editing for length, make sure to provide comfortable transitions through the sections you have cut.
Be sure the writing sample presents a viable, self-contained argument and states clearly your contribution to debates in your field.
Begin and end the writing sample strongly (if it’s a large applicant pool and they ask for the writing sample up front, your first page might be all a hurried reader sees).
Don’t start with a review of the work done by other critics in the area; confine that material to a footnote or footnotes. Begin with an introduction of your own argument.