'Guardians of the Galaxy: Volume 1 and 2" writer and director James Gunn recently revealed his script for the second Guardians film
and offered some insight into the filmmaking process, including how he worked with the crew of the next Avengers crossover movie while making his film.
Website comicbok.com shares that Gunn took to social media writing,
took a lot of notes on what would happen in Vol. 2 before ever starting Vol. 1. I actually started writing the treatment/story on the day the first film came out (Aug 1 2014) and the script was pretty much finished in October of 2015 a couple months before shooting.