'Of all the Beatles, Ringo did the least songwriting. He did, however, write "Don't Pass Me By" (on The White Album) and "Octopus's Garden" on the album Abbey Road, albeit with quite a bit of help from Harrison. The former continued to show the taste for country music that Ringo had brought into the band on earlier albums, such as on Rubber Soul's co-write "What Goes On."

In addition Ringo contributed a number of lyrical ideas and song titles to Lennon and McCartney, although usually unintentionally. One of the most famous examples of this was the title for the band's first motion picture, A Hard Day's Night. Starr had emerged from the studio after a long day of work and commented to the others that it had been a "hard day's..." - before he finished his sentence, Starr noticed that it was now night time and added "night". Lennon and McCartney liked the twisted phrase enough that they decided to use it as the title for the still untitled movie the band had been filming. Another example is the title to "Tomorrow Never Knows."'

from this site.