The first thing you need to do when you're considering backpacking around the world is to establish how much cash you'll need.
 To do this, you'll need to create a budget and an outline.
 Firstly you'll need to determine when and where are you going to go?  Will you travel overseas, to different continents? Or will you keep it cheap and only travel to places in your own country.
 Obviously these decisions are going to affect costs.
  One good way of determining where you're heading and what route is to simply get a large map and to circle the world locations you'd like to travel to.
  This is in effect, the best way of planning a route.
  From there you need to talk to your travel agent to determine whether buying a round the world ticket is a good option or to buy tickets in each individual country - very rarely is this the best cost maneuver.
  Choosing to travel in winter and or summer is going to affect cost as well.
Travelling in winter is nearly always cheaper unless there is of course, some large event going on in the country/continent in which you'd like to travel to.
Once you have some idea on price concerning the air ticket you should then simply just go online and see whether you can get a better deal.
From there, you'll need to work out what it its going to cost to eat, where you're going to stay etc.
 The most important thing is the air ticket, once you have an air ticket - you are well on your way!