Settled.govt.nz - Simple tips to preparing your home for sale.
The List Realty - Their 7-step checklist has several key insights.
MyTrove - Supported by Internal Affairs, a useful guide and means of notifying multiple organisations in one place.
Peter Walsh - A master in psychology and decluttering. He has a website and several books.
Decluttering methodologies - There are a lot! From KonMarie, to 20/20/20. Research, and find what works for you.