Blogging is a great way and also a low cost way of developing an online business. However, when choosing a subject area to blog about far too many online marketers focus on markets that are highly lucrative in terms of potential financial gain. The trouble with approaching blogging in this way is that you will probably end up choosing a subject that you know very little about, therefore have trouble writing about and before long lose interest in.
Instead, forget money for the moment and simply blog about things you love. This way you will find endless topics to write about and your readers will detect this passion and will more likely return to read future blog posts of yours. Besides, whatever your topic, there will always be ways to monitize your content regardless of what your chosen subject area is about.
Remember, build a valuable resource, the visitors will then come and you can then sell them something!