I see so many people trying to "choose a niche" and I think it's been ingrained in us to try and niche down to a level that there is little competition so that we can succeed easier.
I submit that instead of choosing a niche, you choose a MARKET.
Then, you can choose as many niches WITHIN that market as you'd like and constantly cross sell your products, build a list, and build a name for yourself within that market.
i.e. Photography is a market, studio lighting is a niche within that market, natural lighting is another. Also, wedding photography is a (large) niche within that market as well, as is Portraits, Animal photos, boudoir, maternity, etc. etc. etc..
If I chose Photography as my market. I could write a guide on wedding photography, sell it.... then, write a new product on portrait photography and sell that to my past list of customers, offer it on my thank you page of my wedding guide, etc. etc. etc. All the while building myself into a larger authority within my MARKET.
Once you choose your market, find a niche within that market. Hell, maybe you find a niche (like wedding photography) that you can niche down even further.
Create your product or sell some affiliate products... Then, find another niche within your market and cross sell your customers on your new product.
Stop skipping around from niche to niche trying to make yourself successful.
Someone that chooses Koi Pond Building has no opportunity to cross sell their next product if it's How To Improve Your Golf Swing. So they have to start all over again.
The object is to BUILD ON YOUR ASSETS, NOT start as many micro-businesses (that you have to build from the ground up every time) as you can.
Choose a MARKET, not a niche.