Keep a journal. Good and bad times alike, write them down. You will be able to view your past life through the lens of your then-current self. Memories fade, but writing it down can anchor them in some form of truth.
Try writing down just one sentence a day in a notebook. I write multiple things down every single day and it has been one of the most gratifying things I have ever done. Commit to writing down memories to make them forever remembered, including by those who may stumble upon them after you are gone.