There is no point starting a blog on some thing that's already being done! Rob would say "Don't reinvent the wheel"

You need to find a topic that interests you and others. You should try and know as much as you can about your topic other wise you sound amateur ( like me) and your blog will run dry.

If you niche is well taken you could try a set up a sub-niche that's popular.

Will you always have new content? If your posting about a niche and there...

simonb