All immeasurable SEO begins with keyword research. Even if you already have a topic in mind, some quick keyword research can mean the distinction between no organic traffic and a few hundred or thousand extra guests per month. But how do you find the right keywords to target? Even if you do happen to find a suitable keyword, possibilities are great that all your competitors already know about it.
Time to get more precise. If you have some rankings already, look at the other sites ranking for the same keywords as you. If not, start scrutinising for keywords you think might be a desirable fit.