He began writing for radio but switched to television early on. He learned the necessary discipline of writing through radio and in trying to succeed in TVâ€”lots of practice and dedication to the craft itself. He kept writing, constantly, relentlessly, until it made him better, and he never lost that work ethic. His Patterns intro (linked above) deals with that, too.
Early in his TV career he began speaking his scripts into a dictation machine instead of typing them. He mentions that it saved him time, but it probably made a profound difference in his writing voice and his mastery of dialog.