Tailor your music publishing business to a particular scene or genre in order to better approach prospective licensees and record labels. For example, focus on publishing only indie-rock music in order to better identify and brand your publishing business.
Develop your artists' skills to their full potential in order to churn out marketable songs. For example, you can hire a vocal coach for an artist who needs singing improvement or set up a songwriting collaboration between the artist and a hit songwriter.
Advertise your music publishing company in trade magazines, online and in any other outlet where prospective licensees and record labels might look for new songs.
Network with music-industry executives. The more and better relationships you have with movers and shakers in the business, the more likely your song pitches will be noticed.
Plug your songs. Approach prospective licensees and record labels with the artist's songs, doing your best to sell the songs, highlighting hits and offering ideas for potential usage. For example, you could approach a chewing gum company with a song called "Blowing Bubbles" that you feel would work well on a commercial to sell gum.