So, what you need to start your blog and earn on it? Of course the idea. What is interesting writing to you personally, and what, in your opinion, it will be interesting to read or learn the other. Next you need the website. Do not rush to contact the freelancer or professional web Studio, you will have to pay for something that you can do yourself. By using WordPress you can create your website within 5 minutes. You will need a hosting site and domain name. It will cost you mere pennies, but you will be an information portal only if you correctly found a vein — will find its reader.
If you want to cheat a little, and so to speak, to hold a mini survey among your friends to find out what blog theme you to create better, don't ask them what sites they are visiting. You will not help. Don't ask them what articles they read, most likely they are not able to objectively answer this question. Ask them what they are interested in. And if this applies to you — write on these topics and drop a link to your friends.
The fact that people, as a rule, I don't think such concepts as "subject", "article". They have some interests, and that correspond to the subject of these interests and contributes something new, will certainly cause them positive emotions. Their focus is always on the content of what they read and not on where and how they read it.