How to avoid losing a lot of money targeting your audience

In order to avoid losing a lot of money targeting the wrong audience you need to do what I didn't do! We're all told to identify our target market first when setting up a podcast, vlog or blog. I couldn't agree more BUT while I agree that is the right advice, if you identify the wrong market, you may get a big audience but you could end up losing a lot of money, not gaining it. That's exactly what I did. So how do you avoid doing what I did? How do you target your audience correctly for a podcast, vlog or blog?