Passport for someone else

I will be going into the passport office with someone elses passport application as they are unable to get the time off work (we both live at the same address). I have two questions:

- Do I need to bring any documents for the applicant or do I just bring my ID?

- An address could not be completed due to space. Can the address be written on a blank sheet of paper in pen or do we have to complete a special form?