Now that you have 2 or 3 niche ideas that really interest you, it's time to refine them.

If your niche is broad, sure you will have endless ideas of things to both write about and promote, but you will also experience loads of competition. It also makes it much harder to focus on an interest group. You will find yourself jumping all over the place and your readers will be a little confused as to exactly what your website is all about.

Ultimately you want to target a group of people who are interested in learning about a particular thing. By that I don't mean just one product, or one problem to be solved, but you don't want your target market to be too broad and ambiguous.

As an example, if you chose "Health" as your niche, it is just way too broad and unfocused. True, there would be loads to write about, but unless you are a doctor or nutritionist, it'll be very hard to establish yourself as any sort of authority on the subject. Instead, delve into the subject deeper and find a particular segment of the health industry to focus on. You might focus on something that's gender specific or age specific, although this is still too broad. A website about various ways to quit smoking is a targeted health niche

So, define your 3 main ideas down to groups of possible sub-niches and write these down on your list.