If I have nothing to say, I do something worth blogging about. Take a walk, cook a new meal, go shopping...anything. Sometimes it's as easy as looking out my window.
One of my favorite prompts from my first creative nonfiction class in college was "Write about something you saw today". Take 10-15 minutes to free write and actively describe a scene from your day. It'll amaze you to realize what moments stick with you when you're not paying attention.
I also like to borrow ideas from fellow bloggers. To be a better writer, read. There are so many talented and interesting people out there in blogland. Get to know them and see what they're writing about. You never know when something they write will inspire a response or rebuttal post. (I wish I had a specific post when I've done this, but I can't think of when the last time I did it.)
And the neverfail way to come up with a new post: Pinterest. Unpin something and blog about your attempt...success or fail.
Anyone else have ideas for blog posts? I'd love to hear them!