The hubs are scored 1-100. You start off at 50 when it is first published. The score will increase as more people visit your hub. The score will also increase when people leave comments. A good hub you can read on this topic is https://hubpages.com/community/Boosting-HubScores
If your hub has duplicate content that is on other websites or is overly promotional that will hurt your hubscore.
Also do a search on hubscore and you will find many other hubs on this topic.