Reading...
Yes, is certainly will improve your writing. I actually asked this same question to the 16 screenwriters I interviewed for my new book, Q & A: The Working Screenwriter (now available everywhere online). Many of them read Mark Twain, Hemingway, Raymond Chandler, Hammett, Ian Fleming…and a whole flurry of interesting stuff. As for me, I just can’t get into fiction. I’m a non-fiction guy, so lots of biographies and autobiographies.
Jim