Adding the Bridge
The bridge is a transitional element most often found near the end of a song. Musically, the bridge is used as a break from the repeated sections to keep the listener's attention. Both musically and lyrically, the bridge should be different than the song's other sections. A bridge should be a little something extra. It's a place where you can go outside what the rest of the song is doing and push the envelope a little. To build a bridge, you may choose a different melody, chord structure, meter, information flow, or rhyme scheme.
Often, the end of the bridge is the lyrical and musical climax of the song. In most songs, the bridge precedes the final chorus. If so, it's important for the lyrical and musical information of the bridge, especially the last line, to lead to the chorus.
A bridge isn't always necessary. Sometimes a simple verse/chorus format is enough, or a short instrumental leading into a lift/chorus does the job. Use your intuition to tell you if a song needs a little something extra in the form of a bridge.
A bridge can be a great problem solver in a three-verse song that's starting to feel a little ho-hum. Just take the lyric information of the third verse and write a bridge with it.