Be sure to promote your podcast in Yahoo!’s beta service for podcasts, because though it is very new, at less than a year old, it is already very well used.
And, because it is a web-based podcast directory, as opposed to iTunes’ proprietary, software-dependant model, Yahoo! Podcasts assist you greatly with visibility in the search engines.
For [...]

Knowing how users download your podcast can drastically change your marketing methods.

Do they download primarily on iTunes or the host of other podcatchers?
Do you have more downloads with longer or shorter podcasts?
Are they listening via an mp3 player or their computer? (you’ll need to do a reader survey to ascertain this answer)
Do they convert to [...]

Think about your own TV/Radio habits, and tell me, are you an ambient listener?
Jeremiah brings up a good point:
I suspect that many podcast consumers are doing other activities besides listning, as a podcaster, how should you respond?
Write your podcast script or notes to match what your audience is doing. In my experience, they’re intently [...]