Just speak a world and that can be topic for blogging.You can blog on topic.But it should be your niche.It does not matter if you are doing it for fun.Because who will read your blog-mom,dad,friend,bro,and some knowledge hungry people,if it is of there niche. But when you blog to earn online money,you should be careful to choose your domain name.If you are thinking of writing about Google AdSense,even though its your niche.Its very difficult to earn from your website.How many people know about AdSense,even though they know about Google as a search engine.Here is the first cut to your audience.Who will search for you? Only those people who are already adsense publisher,and want explore new tricks and tips to earn more. These people are very well familiar about Google ads on your webpage.There is a very rare chance to get a click from them.Let us compare with other topic say dating site.If your site is about dating.People who visited don't know about all those stuff,and natura