The optimization process and recommendations:

1. Avoid Selecting Unnecessary Columns (query line: 25): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
2. Avoid Selecting Unnecessary Columns (query line: 6): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
3. Avoid Selecting Unnecessary Columns (query line: 16): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.

The optimized query:

WITH artists_ranked AS (SELECT
        artists_ranked.artist_id,
        rank() OVER (ORDER 
    BY
        score) rnk), not_listened_songs AS (SELECT
        * 
    FROM
        songs 
    WHERE
        NOT EXISTS (SELECT
            1 
        FROM
            listened 
        WHERE
            listened.song_id = songs.song_id)), shuffled_songs AS (SELECT
            * 
        FROM
            artists_ranked 
        JOIN
            not_listened_songs 
                ON not_listened_songs.artist_id = artists_ranked.artist_id 
        ORDER BY
            random()) SELECT
            DISTINCT 
                ON (artist_id) * 
        FROM
            shuffled_songs LIMIT 1