Well, some secrets there. Here let's consider.
First of all, you need to intelligently approach the choice of topics and to clearly assess their own capabilities. This is difficult to do for beginners who have little understanding of how to develop a blog. But the problem is that when you create a blog you need to have a good understanding of how to proceed in order to achieve good results. That is some experience here would not hurt. But for beginners it is not, so you have to act at random. This problem is almost unsolvable, because without real experience will fail to objectively assess their own capabilities and to make algorithm development blog. The only thing that can help in this situation is the advice of an experienced mentor.
You need to choose a theme, which in fact has the money. If the subject is of no interest to advertisers, and buyers few, the money did not succeed. But the problem is that the most profitable topics long ago dismantled by other bloggers and other webmasters. This indicates the high level of competition. So, if you create a blog on a profitable topic, where competition, to promote it, most likely, will not succeed. It is much better to choose something in between, where a small competition and there is at least the average income, or rather can be, because the blog is not created yet.
When choosing subjects it should also be competent to assess their own skills and knowledge in the subject. If you have something to tell the audience, it is safe to create a blog, but if your own knowledge is not enough, it will be difficult to develop a blog. Note that people love to listen to the professionals. If the selected topic can be considered as a professional among a certain audience, which also should be interested in receiving content, you can create a blog. But if your knowledge is quite superficial, most likely will not be able to win the trust of the audience and it is a serious problem that is very common among beginners.
But creating a blog is not enough. Need actively to develop and promote, attracting more and more readers to it and thus expanding the audience. It gives the blog more chances of high earnings, because the more traffic, the more income. Therefore, to promote so important. Just many people forget about that, concentrating solely on the content of the blog content. They believe that this is enough for search engines to notice their blog and started his high rank. This view is erroneous. One who is not engaged in the promotion, you will not be able to achieve good results in terms of popularity and earnings, respectively.