Well, that depends, what are you interested in?
If you look at my profile you'll notice a lot of hubs about Autism, Animation, and Readind/Writing, This is no accident. Stop and think for a little. Do you like sports? Who is your favorite team? Why? Write a hub on that. Do you enjoy musicals? Make a list of your favorite musicals and why they're your favorite into a hub. Ask family and friends (or Facebook) what they're interested in, write a hub on that. Do you or your family have a super secret recipe? Write a recipe hub. Which cell phone is the best on memory? Graphics? Performance? Write a hub about that. Write a poem.
What are the top apps for a smartphone to you, why? Share a story of a small miracle. What are some of your favorite television shows? Maybe you can turn your profile into a review profile. Have you tried something recently that was really good or really bad? WRITE ABOUT IT!
There's so much to write about, look around Hubpages for ideas (feel free to look at my hubs). Maybe someone wrote a hub poorly or didn't answer all of your questions. In this case you can write a "better" one than they did. The options are endless. Let your creativity flow!!!