Get Noticed Media

I Run A Small Publication - 20,000 Print Run, Estimated 30,000 Readers. However, I'm Having Difficulty Attracting Attention From Advertisers. I Understand That All 'brands' Use Media Buyers And Advertising Agencies.

How Should One Best Present A Publication To These Agencies?

I Understand It Is More Useful To Be Favored By These Agencies Than Their Clients, Is This Correct?