What should you do before short trip or journey to the end of the world?
I advise you to give yourself 2 months for preparation.
Close your affairs in the country of residence (if you are going for a longer period: terminate your employment contract, telephone, contract with your landlord; authorize family members to handle official matters in your name if necessary). Prepare the necessary documents for travel (i.e. passport valid for a minimum of 6 months from entering the last country). Scan them all and send them to your email (it could be useful in case of theft or loss of the original ones).
Research online or go to the nearest Vaccination and Travel Medicine Center. Check what vaccinations are recommended for your destinations (start at the latest one month before the travel). Before my journey to Southeast Asia I got vaccinated for hepatitis A, typhoid fever, cholera, rabies (since I spent a month in the Thai jungle) and Japanese encephalitis virus.
Note: Vaccinations are not mandatory in most countries, just recommended. For the peace of mind it's worth take them though. It could be pricy. I spent over 500 euro on them before traveling to Asia.
Like vaccinations, insurance is ussualy not mandatory, but I don't think any of you would want to expose your family for high medical costs and medical transport.
I recommend the post Must have for travelers - what to take with you to learn more.
If you are goint to travel for more than 2-3 months, it is worth waiting with the purchase of a return ticket for later. Tickets are the cheapest about 2 months to 2 weeks before departure. Besides, your plans could change and maybe it would be worth staying a week or two longer in a given place?
I recommend https://www.kiwi.com/en/ for searching for cheap plane tickets.
Consider writing a travel diary or blog. It will be a great souvenir and will make you feel less lonely (if you're traveling alone).
There are many such cards on the market today. Instead of paying for multiple conversions, choose a card for yourself and safely use ATMs around the world at the lowest cost. I use Revolut.