I have experienced writer's block so deeply that I read every book the library had that even tangentially discussed it. I was unhappy with the responses, which boiled down to "get over it" or "it's not real." It is real, and saying "get over it" solves nothing. Once I was able to climb out of the darkest of writing caves, I wrote Dear Someday Writer to include some of what I've learned about writer's block and how to get out of it.
Character is the most important aspect for me. I have to embody the character in a way similar to an actor who follows method acting. Generally, I have to cogitate on the character and either the opening or ending of their book until it is so visceral to me it's like watching a movie. That's when I can start writing the book.
"There is no try, only do." Yoda. I would tell my younger self this quote because many writers spend too much time in their heads on self-doubt or other worries that get between the writer and the page. I would want my younger self to just do it and much sooner than when I started. I would tell other writers the same thing. It's never too late to start writing, but if you keep putting it off to "someday," you will never write. Today is a good "someday" to start writing.