When choosing a niche, choosing an interest that will sustain your attention for the long haul is of paramount importance. If you're not really interested in your niche, it will be nigh impossible to sustain the level of attention required to create a successful website.
The pioneer days of 'slap up some html and become an overnight success' are long gone. Unfortunately, many of those 'pioneers' are selling you years old information at exhorbitant prices trying to convince you that following their 'formula' will have the same result. It won't.
Once I have decided upon a niche, the second thing I do is determine if it is viable. Determining if a niche is viable is not a journey into LiveChat to ask a bunch of strangers who may not have even been on the Internet as long as you about their 'opinions.' Nor is it asking in the classrooms - most of those other people started when you did.
This is your business. Were this a brick and mortar business, the bank would require that you do market research and develop a business plan before loaning you any money. You should do the same thing even though it is your money at risk when starting an online business.
By this point (choosing an interest), you should be completing the keyword training and searching for long-tail keywords that are appropriate to your niche. My personal thresholds for keyword research are different than what is recommended by Kyle in the training.
I try to look for keywords that have 50 or more traffic (not searches) and 50 or less QSR. This is my personal technique and I am not recommending it over what is being taught here. Kyle/Carson are very experienced marketers and I encourage everyone to follow the training 100%.
The fun begins once we have our long-tail keywords (I recommend five for this phase)