My ideas are sometimes inspired from my everyday life, sometimes curiosity about something I've heard, sometimes from a desire to share something I know, and sometimes from a question left in comments to one of my hubs. For example, we successfully potty trained our beagle puppy (not an easy breed to train) so I wrote a hub about it. One day my daughter was home sick and I remembered how my mother would give us ginger ale to make us feel better, which inspired me to write about the health benefits of ginger. And, lately I've noticed how some hubs could be so easily improved in terms of seo if only writers knew simple steps to follow. Since I have knowledge of html and web design I decided to share what I know. On those hubs I have gotten questions, where my answers to them were so long that I decided to write a hub about it instead.
One thing I do is keep a notebook that I jot down any potential ideas. This really helps when I am ready to write and need an idea.