I just pick subjects that interest me at the moment as a new hubber myself. I find it easier to write about things that I know something about and that are easy to write about. With so many hubbers online someone is bound to read whatever you write at some point. I have added myself as a follower and look forward to seeing what you come up with. You will find once the first hub is written and you have browsed and read other peoples hubs a bit ideas will be keeping you awake at night and it will become addictive!!!!!!!
If you are really stuck though there are lots of hubs about this just search "topics to write about" in the search box and have a browse at a few to get some ideas flowing.