I guess there are different ways to prepare a trip like this. I don't know which way is the best but to have the motivation and goodwill is the best start.
Then the preparation of your bike, reading guidebooks, getting all the papers (passport, visas, carnet de passage, international drivers licence, travel insurance, etc.), vaccinations, updating the gear (camping stuff, spare parts) takes a long time. And even if we are "experienced" travellers you are always short of time....So start long before your departure date...let the fun begin...
Preparing the bike. New oil and filters, chain, sprockets, tyres, brakes, etc. Planning route, reading guidebooks, making scedule for visas.
Getting all the necessary vaccinations (tetanus, Polio, Typhoid, What to take or what NOT to take? That's the question.
Hepatitus A, B, C till Z, BCG (tuberculosis). Look that syringe size...Ouch!