1. Write high quality content. Make sure there aren't any typos in it.
2. Make sure there are enough words - try for 500 at least.
3. Make sure there is a good ratio of words to ads. I try to provide information - and sell stuff on the side. Don't just write hubs to sell stuff.
4. Get people to read the hub and vote it up - you can do this by asking questions, answering questions, participating in forums, and commenting on other people's hubs.
5. Give it time. Most hub scores will go up over time.