All input elements of type "file" 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

Upload your file: <input type="file" name="the_file"/>

Right

<label for="the_file">Upload your file:</label> <input type="file" id="the_file" name="the_file"/>