To write an amazing application, the most important thing is to first read the host and position descriptions. Then you’ll know what kind of person they’re looking for and a little more about the activities you’d be doing. This will also show the host that you prepared well!
Say a little about yourself: why you're traveling, why you chose that area and that specific location/host, where you've been. Just a brief summary about who you are and what you're looking for!
Then include a bit about your life experience: what you study or studied, any kind of work experience (even if it’s not at a hostel/NGO/farm). Your life experiences will show the host several other things about you and how excited you are to take that next step.
Also, comment on the activities you will do: ask questions, let the host know that you are aware of everything and share what you can do to add to the team of travelers and just go \
But remember: there is a difference between taking your questions and making a questionnaire. Make sure that the information you need is not in the job description or even on the host site before you ask, okay? The best thing is to do a quick online search on the host before confirming anything. Good luck!