To improve the score naturally means editing. Hubs are rated two ways. It is read at a human outsource known as MTurk at Amazon. People read the article and rate it in three categories. The rating criteria can be viewed at the following link. The other is it is crawled by bots or assessed by a algorithm looking at the Hub with computer language only for the format, form, and the text.
That link will lead to the criteria for an informational Hub. At the top left is a hyperlink to view the criteria for a Creative Hub like short stories and poetry.
For both there are three areas of focus. They are:
Grammar and Mechanics
The Rating guide should be self-explanatory. A suggestion is look at your score and then look at that first number for the Rating. For instance a score of 60 - 70 look at Rating 6. HubPages suggest a goal is the rating 8 especially for a Hub to be moved to a Niche Site.