Every budding blogger sooner or later faces an important question about the niche he should choose for his blog. Some bloggers prefer to blog just for fun or hobby and some blog purely to make money out of it. If you fall into the latter category, it is imperative to give some serious thought about correctly choosing your blog niche. The success of your blog heavily depends on how you've selected the niche of 
#1: Personal Interest
If you are blogging about a topic you love to the core and are totally passionate about, you have already won—half the battle. The first and the most important thing is to select a topic that you love to explore—read—and talk about.Readers are only going to come back to your blog if they find the content appealing and useful, and you can only serve such content when you are comfortable and expert in your domain.
You may also lose interest in generating fresh content—in the long run—if the chosen niche is not one of your favorites. Having a favorite topic (niche) in hand implies you'll be able to consistently generate useful content—for the target audience.
#2: Popularity
Assessing the popularity of the chosen niche is the next obvious step. If people are not searching for the topic you're going to blog about, then no matter how hard you work—the results will never be promising.Start analyzing with search engine results. Google the first keyword that comes to your mind related to your niche and see the results.
This method will give you a fair idea about the two important things associated with the niche. How much content about that topic is on the internet and does it have some advertiser base—or not?
You can see both the indications in the image above marked by red arrows. A large number of results count suggests that the topic is quite popular.
And, if the result page also displays a healthy list of advertisements, then rest assured that your chosen niche is highly competitive.
To sum up, if people are not looking for that topic on major search engines then your blog is a—dead duck. Working relentlessly on such a blog will be a fruitless exercise.
#3: Profit Potential
The popularity of the topic alone doesn't mean it can reap your profits. The most critical thing is to look whether it has sufficient advertisers' base in major PPC advertising networks.Google Adsense and Yahoo Publishers Network (YPN) are the two most popular PPC programs. Google has provided Google Ads Keyword Tool which also includes Google Ads Traffic Estimator to look for high paying keywords related to your blog niche.
You can use this tool to get a fair idea of the traffic and average CPC for the relevant keywords for Ads/Adsense. Although the provided data is not an accurate estimate, still it will give you a fairly good amount of data to assess the earning potential of your niche blog.
For a more accurate keyword research, you can use professional tools like SEMrush and can get a list of all the vital search marketing data—related to your blog's niche.
#4: Content Availibility
To keep running your blog, you need fresh quality content—at a consistent pace. Some bloggers start very enthusiastically, but soon they end up searching for fresh ideas for their blog.For making a profitable niche blog, you have to feed it with new and useful content—diligently.
Choosing a niche that has a scope to generate a vast amount of content on a wide range of subtopics is a wise decision. You can subscribe to news bulletins, discussion forums, and can ask your peers in the blogosphere to get new ideas and topics for fresh new content.
Give some thought before you start posting on your blog, as it will be the deciding factor in the success of your niche blog. Posting—just for the sake of posting—is not going to work. Check out these free blogging eBooks to equip yourself with all the basics of niche blogging.