You should make an appointment before visiting him.
Literal
Promise-do-[after-てから] him [obj-を] visit-[should-べきだ].
~てから ('after doing') combines the te-form with から to mark sequential order — 'after doing X, then Y.' Clean demonstration of a core A1-level sequencing construction. 訪問する ('visit') is the Sino-Japanese formal verb; everyday Japanese would use 訪ねる or just 行く.