Whenever I get an idea of a topic I could write about I write it down. Even though I write daily I have managed to accumulate rather long list of potential topics. There seems to almost always be something to write about.
On the rare days I can't come up with anything I then resort to this list. Sometimes it's hard to remember what I was thinking about writing some of those few words I have scribed there. Other times I find topics that feel oddly familiar... I feel like I have written about this already.