By hubscore I assume you mean the score on your individual hub.
Actually I have noticed many hubs newly posted having scores in the 50s range. And noticed barely 3-4 scattered on the latest list having 65-70s range. I began to notice their titles and realised that their catchy topics (sure to have interesting hub content) is the reason of the higher score to begin with.
I think a hubscore of 75 is good in my opinion but if that's the score on your profile...means it can be improved.
These hub scores gradually go up as we get comments and affirmative reaction + traffic. Mine generally is tough to reach the 90 mark, but my hubber score has consistently stayed above 90.
If someone has a Hubber score of 75 generally it can mean that either:
1. One is still brand new on hubpages and once more original quality hubs are added it can be seen to gradually go up.
2. One needs to increase the amount of hubtivity happening from ones side
3. Make useful, insightful answers
4. General conduct/good behavior
5. Keep writing original articles with free-to-use or original pictures.
6. Once quality traffic comes in, you are on an upward curve.
In general as everyone here says, don't worry about ones score...do their best and leave the hubscores to keep ticking to the favorable side.
Whenever I post a hub and if it attracts a decent amount of comments, I have seen it jump up to minimum 5 points....then as the comments lessen after a few days I see the score stepping down 1 by one every hour if there is no activity from my side. But if I am doing a lot of that,,,the points dropping are slow. I find the quickest jump up depends on a popular new hub and traffic to your hubspace. My take!