Luckily, I was involved in the advertising world prior to 1994 and had many agency and client contacts. I was able to think about the best place for my companies to be (per sales and exposure to the right group), and made it my mission to make a name for them... and it happened! I've done this time and time again for the sales department of the companies I worked for. Here are my suggestions:
Volunteer your time. Get involved, in a major way, with one or two trade organizations. Volunteer to run a program or get a speaker or run a breakfast meeting, etc. in whatever city you are in. For example, in the New York City area:212NYC and The Advertising Club of NY.
Know your marketplace. Be on top of your game. Read the trade publications weekly/daily, and don't be afraid to contact those people you might want to work with--and just say "hello."
Put in face time. Attend every media-related event in your area of expertise. Attend major organizations' monthly meetings/events. Sign up and attend at least two shows a year that are pertinent to your area of expertise. Host media sweeps two times per year: your group meets with 10 agencies and presents your Web site's "pitch" within a two-week time period. They need to know who and what you are all about. Bring snacks or lunch!
Hire the best and compensate accordingly. Use your resources and get the BEST top-level executive to help you create a well-oiled machine! And hire interns. They don't cost much (sometimes they're students who will work for free to get real-world experience) and can really help!
Follow-up. Ninety percent of the game is follow-up and building a great relationship! Send thank you/holiday/birthday notes to those clients with whom you are working-- and those with whom you want to work. Be on top of an account once they are partners with you--that's key. Remember, 80% of your sales come from 20% of your customers. Say "Thank you" whenever possible.
Smile. Life is good. A good attitude is contagious.