All input elements with a type of "checkbox" should have a corresponding label element. Screen readers often enter a "form mode" where only label text is read aloud to the user, and missing labels can make a form unusable in these cases.

Example

Wrong

Sign up for our newsletter: <input type="checkbox" name="newsletter" value="yes"/>

Right

<label for="newsletter">Sign up for our newsletter:</label> <input type="checkbox" name="newsletter" id="newsletter" value="yes"/>