Incorrectly regarded as goofs: In common with many other sitcoms, details of characters' back-histories change through the life of the series. We don't count these inconsistencies as goofs in long-running shows.
Continuity: In some episodes, when exterior shots of the fictional "Monk's Diner" are shown on two sides, you can see the real name, Tom's Restaurant.
Continuity: You will notice that on external shots of Jerry's building there are insect screens on the windows. However, these are never evident whenever any of the cast occasionally lean out the window whilst the scene is being shot from inside Jerry's apartment.
Miscellaneous: Jerry's apartment number changes in the beginning of the series a few times before becoming 5A permanently.
Miscellaneous: Newman's apartment is shown as 5F in one episode, and 5E for the rest.
Continuity: Jerry and Kramer's apartment building address is said several times to be 129 West 81st Street, but the awning outside of the building has the address 757.