wow, some great advice here.
Here are my 2-cents...
I could not agree with the sentiment that you need to stick with what you like and know. This will serve several purposes: a) make it so that it does not seem like a job, and b)allow you to find your "voice."
This last element is important because IMHO trust = $$$
The second your reader begins to trust you, you will begin to see a difference in your bank account.
So, get started and put a blog on that niche that you feel strongly about. A great motto is: "find something you love to do and you'll never work again."