You could write on anything, from fashion to technology, geology to politics, economics to history, consumer electronics to real estate, family or kids to relationships, dating or health, sports or current affairs to news, events, photography and anything that interests you.
Bloggers who have an astute understanding of what they are writing or the larger domain will always do well. Blogging is not just writing. It is a fine combination of writing acumen, knowledge, specialization, awareness of latest updates and an understanding of what people or readers are looking for.
Choose a niche that you are comfortable with and equally important is the readership. Do not pick a niche that no one is interested in. You can write a blog on such a niche to satiate your own desire but such a blog will be hard to monetize. You can only monetize a blog for profit that will have substantial traffic. Microbiology or nuclear science, applied mechanics or even the history of textiles would not be appealing niches, even though some interesting posts can potential get thousands or hundreds of thousands of hits. A niche must be perennially popular for the blog to be monetized for profit. You need sustainable revenue and not a onetime windfall gain, although the latter too is welcome with the sustainable profits.
There are many ways to monetize a blog. One of the most unpopular and ineffective methods is subscription. We live in an era when information is free. While you can have your content and intellectual property protected with copyrights, you cannot really prevent the information from being available in some other form. Reproduction of information in non-plagiarized forms will always happen. Since there is no dearth of information, subscription has not really been the most successful way to monetize a blog.
