Often, bluesmen end a song by working through a more complex version of the turnaround they were using, but ending on the I chord rather than the V chord. This creates a sense of closure to the music.

The V chord creates a sense of anticipation in the listener—they are waiting and ready for it to resolve back into another go-round of the song, so you never close on the V. The I chord is more of a punctuation mark and the listener is ready for the song to terminate at that chord.

For a longer ending, you can work back and forth, a measure or two at a time, between the V and I chords, building up to a final closure on the I chord.