They say that nothing is scarier to a writer than a blank page. Of course, it's not the blank page that is really what horrifies us, it's the blank mind, the feeling of being sat in front of your computer (or your paper, if you're really hardcore old school) without a clue what to write about. For most writers who may have long since mastered the ability of putting words onto the page in an eloquent manner, it is coming up with ideas to write about that is the true challenge, and that's the same for everyone, whether in the self publishing game or otherwise.
If you're writing an autobiography, of course, all you have to do is look at your own life and find something that might be amusing to write about. Fiction, however, is a completely different kettle of fish. What if you're writing something entirely fictional, such as science fiction or fantasy? The trick here is to look around you but look beneath what you are seeing. That old bloke you pass in the street every day, what if he was a serial killer? What if you got on a train and rather than take you to your mother in laws', it took you into a parallel dimension? The trick is to keep generating these premises, no matter how whimsical, farfetched, or absurd they may seem.
p.s. Not all your ideas will work, but one or two might just start you down the road to a great story.