The first step is documenting your audience and the amount of traffic your podcast attracts. With this information, you will be able to develop a press kit which you can use to approach potential sponsors. They will want to know that you are speaking to their potential buyers on a regular basis.
As for podcast statistics, you will probably need your raw log files in order to capture the total number of downloads for each episode. Then you can aggregate them to create your total monthly downloads. These downloads will include both new shows and older shows as people do not often listen in order, or find older episodes and listen directly from the web site. This number will show you the number of “impressions” you might be able to fulfill for a given sponsor.
Make sure when you develop any sponsorship campaign that the sponsor has a way to track exactly how many buyers came from your podcast. There should be a unique product code or coupon which they can track on their end so they don’t have to rely on you for that reporting. If they are tracking it themselves they will be much more trusting of that info.
Here is an example of a podcasting press kit – http://www.businesscast.ca/media…
Proving the numbers can be difficult, but I like the idea of using a product code or coupon. Building podcast audience through proper syndication is also important. More on syndication here:
http://mobilecastmedia.com/blog/how-to-maximize-reach-of-your-podcast-via-syndication-through-itunes-and-social-networks/