Price out possible RTW itineraries and tickets far in advance of your trip. This way, you have a idea of what your trip airfare will be and you can budget accordingly. A year in advance is not too early to start getting prices and researching which hubs are cheaper and how routing works. 3 to 6 months in advance is the ideal time to purchase your Around the World Ticket.
Start planning your trip here:
https://www.bootsnall.com/tripplanner.shtml