There are a lot of people who actual use WordPress as I do here on this website. So a real good subject would be to create a website about for example the plugins you can use in your website.
Not only to explain what the best once are (And trust me there are a lot that are free and are really good) but you can also talk about how you can use those plugins to make a profit with blogging.
And the more interaction you can get with your readers the better it will be.
What do you think of this idea ? Let me know if you have ANY comment ?