PA work isn't really the most direct job for a writer because production assistants tend to be focused on production work. Ideally, I'd recommend (in this order):
#1: Writers' assistant on a show. This is the "PA" of the pre-production world. Here you'll be delivering coffee and scripts, depending on the show you could be in the writers' room, and you'll be in a good position to create relationships.
#2: An assistant for a writer with a deal.
#3 An assistant/intern for a production company that produces television.
For these jobs, like most, you really need to know someone. That's why I suggest you focus on getting a livelihood job, building relationships, and then going after an industry job. ALL THE WHILE WRITING. Always be writing!
For more tips and articles by top entertainment industry coach, The Greenlight Coach, visit www.theGreenlightCoachBlog.com