GDL is a very user friendly airport. It is located in southwest "corner" of Guadalajara and is at the end of a highway "culdasac".
There is a multistory parkade and (I recall) an Oxxo directly in front of the passenger terminal. I have always rented a car, so I have never used the parkade. For a car rental, exit the terminal, bear left around the parkade, and about 150 yards are 6-7 car rental companies.
I have always had an "adventure" turning onto the highway from Guadalajara to Manzanillo -- road construction, inadequate signage, and my personal preference for travelling without road maps have conspired to to making the correct exit improbable on my first attempt.