Never start something without knowing what it would take for you to call it successful.  What is it that would make you feel like your podcast is successful?

Is it achieving a certain number of listeners?
If so, decide the number and track your subscribers to see what they seem to like and dislike. 

Is it adding value to you site?
How do you track this?  What are you doing to determine if you are successful here?

Is it bringing in new business?
Set up a unique referrer page on your podcasting show notes.  How many people are ‘converting’ due to your podcast?

If you don’t know where you want to go, you will probably not get there.  Know what you want BEFORE you begin.  Of course, you can change course along the way as you come to understand the medium more, but you have to be on a course, to change course.  Don’t just podcast because everyone else is doing it.  You will not be successful unless you actively plan to achieve certain goals, but only you can determine your goals and how to achieve them.