Brainstorming blog ideas is the first step. What are your hobbies? What do you like to do? Is there something you know a lot about? Think about all the things that you could possibly blog about. You will want your blog to be somewhat focused on on topic. The more focused the blog, the better. If you have a blog with sports related posts, and investing related post, the investing posts might show sports adds that wont get clicked, and the sports posts might show investing ads, that wont get clicked. It would be better to create two separate blogs, one for sports, and one for investing. But you don’t want to use a topic that is TOO narrowly focused. If you create a blog about a very obscure topic, you might get little traffic. But then if yours is the only site about the topic, you might get all the search engine traffic for that topic. It is always good to find a solid niche that is untapped. But if there are only a couple hundred people in the world interested in the topic of ‘green frapplehammers’, you might get all that traffic, but it might not be worthwhile.
Will people want to read about your topic? If you create a website about your dog, and post all about what your dog does each day, chances are many people wont want to read it. But say your dog is an Airedale Terrier. You could create a site about Airedales, and write posts about selecting puppies, breeding, training, breeders, dog shows, etc. Other people with that type of dog might be interested in reading your posts. But will you run out of things to write about?
If you travel a lot, you could create a travel related site. You experiences while travelling are bound to be different than anyone elses. And everytime you travel, you will have new stuff to write about.
Another thing to consider is what is the earnings potential of the topic? If you want to do a site about books, think about how much books sell for. A new book sells for $10. Advertisers are not likely to pay alot for your to display ads that might sell a book or two. But for a site reviewing x-ray machines, or something expensive, advertisers might be willing to pay more per click. But do you know anything about x-ray machines?
Now that you have come up with some ideas, consider how much you will have to write about each topic. If the topic is something that you might be able to write a half dozen posts about, and thats it, it is probably not a worthwhile topic.
Some topics that you will definately want to avoid are things like drugs, sex, violence, hate sites, anything like that. Most advertisers will not allow their ads to show on your site. So if your hope is to make money from your site, you will need advertisers.