All input elements 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

Enter your first name: <input type="text" name="first_name"/>

Right

<label for="first_name">Enter your first name:</label> <input id="first_name" type="text" name="first_name"/>