Hey. I got somewhere with my PS using this system
First jot down all the things you want to include. Start with the basic questions (what I like, dislike, why it interests me, etc.) Don't be hesitant here - pen your thoughts down. After that try correlating all of them with any achievements you did and this should form your first outline for a PS. Write a draft and repeat this process again and again.
Ideally the ps should be very subject specific, so do not include any unnecessary details.