Listen to the performance of the song. You often can identify the pattern of rhythm in the lyrics simply by patting the steady beat of the song.
Look at the way the lyrics are arranged. Patterns such as ending lines with rhyming words often hint at the rhythmic scheme.
Read the lyrics aloud. Begin to tap a steady beat as you read.
Read the lyrics again while tapping the beat. This time pause at each beat and mark the beat on the lyrics sheet with a slash or vertical line.
Read or sing the lyrics once more while tapping the rhythm marks that you created. If it seems to fit, you probably have correctly identified the rhythm within the lyrics. If there are awkward points in the song, change the rhythmic marks as necessary.