Looks like you already have some hubs, which is a great start. Next, try finding hubs written by other hubbers that interest you, and leave a comment on them with your thoughts. Comment on a few hubs each day.
Go to the forums and browse the topics, respond to anything that interests you, or start a new topic.
Asking questions is also good, as well as answering them.
I noticed most of your hubs are written with some good info, but also for the backlinks to your website. Which is fine, but on hubpages, the more 'good' things you do, the higher your hubscore will be. So try writing some hubs that don't have links to your website, and you might see your hubscore jump up past the no-follow threshold.
For more info on this check out this article:
The good news is it shouldn't take you too long to get above 75, as long as you put some quality work into things on hubpages. And in my experience, as long as you maintain good quality, you should have no problem staying above 75. My score has not gone below 93 in ages, and I am not as active on here as I want to be.