The author score? Well, if that's your referring to then basically you need to publish hubs fairly consistently. Be active in the forums, answers, make comments on others hubbers hubs. Comment back if they comment you.
You want to be active and publish good quality hubs. It also depends on how much traffic you get. The individual hub score always starts at 50 when you first publish so don't worry about that. It will eventually get its average score depending on the quality and relevancy and how much traffic you receive to it.
If you copy,spam, or have inappropriate content the score of the hub can take an all time low. So be careful of that.