Forms should include clear labeling. Otherwise, your end users will not know what is expected or required of them. The recommendation is that form have external labels that indicate the purpose of the field. Placeholders are discouraged because they may be confusing to users who often seem to leave placeholder text as they submit forms. WebAIM offers recommendations on how to code forms. A11yideas, an initiative from Deque, accessibility consultants who are leaders in the accessibility community, offer advice on form field groups from the perspective a screen reader user.
Inside Iowa State published a thorough story on how to create accessible, usable and attractive forms.