Research: In order to plan a trip you should be spending hours researching: how to save money, best places to stay, cheapest way to get around, the currency conversion for each country, how long you’ll approximately need in each place, where to go once you’re there, and the weather in each place.
Planning: After you get this information you should be sending tons of emails (to possible hosts), plotting out where your money is going to go and making sure you have enough for each thing on your list, creating an approximate itinerary, and buying things you’ll need (backpack, walking/hiking shoes, etc).
Preparing: Once you’ve got everything planned and ready for your trip, the next thing is to prepare your mind. You can never really prepare yourself for a first time backpacking trip, but watching documentaries, reading articles/blogs, and reading books will definitely get you thinking the right way. Not only will this get your head in the right place but you’ll get very useful tips and information.
Now these 3 steps are very important, but things won’t always go as planned. This is okay. You should prepare for your trip to make sure you can survive and to get information, but I strongly believe in going with the flow. Try to leave a few extra days between each place. You may end up making really good friends in one place and want to stay there longer or hear about a place not too far off your path. You can plan out the major cities you want to hit, but don’t try to make a daily itinerary. One of the best things about backpacking is having the freedom to go wherever you want whenever you feel like it, and stay there for as long or as short as you feel like, and you won’t know this until that moment.
There are different styles of backpacking, so this is just my personal take on it. I have friends who only planned out their destination spot and their journey was hitch hiking all the way there. This is definitely a much more fluid style, it just depends on your personality.