It probably helps to have at least 100 hubs, preferably on subjects that people want to read about. I think it also helps to write on a variety of subjects. Not everyone has the same interests.
Also its helpful to participate in forums and answer questions. Reading the hubs of others and making good comments is another way.
When your hubberscore gets up high-- a lot of people will follow you without even necessarily reading your hubs. (This kind of following is meaningless, by the way.)
Why do you want so many followers?