Try to get in as much trekking and multi-day trekking as you can in your preparations, along with getting used to all of your gear you will use on the trip.
You can gain mental strength from your physical training and all the preparation you put in. Try to get in as much trekking and multi-day trekking as you can in your preparations, along with getting used to all of your gear you will use on the trip. Get yourself mentally prepared for the developing world.