I had a hard time writing my ps also.  I had alot to say, but didn't know which points are important to make, and how much space should be devoted to each area of interest.  So I bought a book, titled something like: Medical School Sample Application Essays.  Suppose to be a compilation of real people's essays.  Some of them were really good, and had similarity to my own experiences.  they gave me a good place to start my own essay, and also how to organize it.  Just search on amazon.com, and I am sure you will find a few to help you out.  
Even thoug nothing can be perfect, it is nice to try  😀 
I went through at least 5-6 drafts on my ps.  my premed advisor also read it over twice.
PS is very important, I was asked about things in my essay at every one of my interviews.