Actually you have to analyse it by looking on your business competitor.

You need to find a niche with a relatively high demand (or else you'll not be able to make money in it), and a bit of competition is the first sign that there is money to be made. Even in competitive niches there are still opportunities if you find the right keywords. So once you choose your niche, then you need to do keyword research to find keywords with reasonable number of searches, but not too much competition. Start by using the Google keyword tool (free).