I was worried about my hub score as well when I joined, which was more recently than your arrival. From my experience, my hub scores fluctuated first but then started to slowly rise and now they have a quite steady curve they follow.
I'd say just write quality articles, that helps. Don't you ever spin an article you find elsewhere on the internet, and do a google search before you write an article to see whether someone has already written about it before.
For the quality part, I think a good advise is keeping paragraphs below 5 lines and keeping continuous text blocks below 5 paragraphs. You can always break the text with pictures, videos a poll or such.
There's also impeccable grammar, that helps a lot I presume albeit I can't really speak from personal experience, I'm a non-native speaker and my grammar has been stuck on a flawed-good level for quite a few years now, not sure whether rewriting some of my earlier articles would even help at the moment.
Another thing is not to overuse amazon and ebay capsules. They may be tempting, but you aren't going to get the traffic for actual income for quite a while.