The first thing we had to do was read lots of books. Lonely Planet, Fodor's, The Rough Guide and Auckland Public Libraries were invaluable. From there we started pulling together a travel path and rough outline. Then it was on to booking.com and actually making some bookings for where we would be heading. Booking.com was great as we could make bookings with easy cancellations.
That meant we could change our length of time places really easily as we made changes based on what we wanted to do in each place.