Me and my best friend are going travelling next year, places such as Australia, New Zealand, Thailand, Asia and South America.
Accomodation wise, what is the best way to go about it, should we bok in advance or just get hostels everywhere?
Hostels are accommodation. In high season you need to book ahead as they start filling up. Other times you can just walk into one. But you get the best choice by booking in advance, and that also means you have a place to go straight to and you don't have to drag a backpack or whatever around looking for a place.
The Accommodation link at the top of the page is good for hostels, and will give you some idea of prices. Ideally you will want somewhere reasonably quiet at night and close to public transport. Also if you ever have to check in very late or very early, somewhere with 24 hour check-in.
You can get a Round the World ticket, travelling to NZ one way and coming back the other, though travelling via South America is the expensive way. Before you book, check on weather at destinations so ideally you'll have at least reasonable weather for sightseeing and especially for beaches.
See tips on round the world travel