I don't think there is a set formula for reaching 100. I've done it once (that I know of) and it didn't last very long. Since the site (and the internet) is in a constant state of fluctuation, getting and staying at 100 is not easy. But if you want to get a shot at it, then focus first on posting quality, original hubs. HubPages hates duplicates and loves longer, error-free, articles. So always make sure to run a spell check and really exhaust each subject. And being active helps. You don't have to be on the site 24/7 but each time you log in to check your profile, take some time out to answer a question, make a post on a forum, or rate/comment on some new hubs. Being active in the community will help you earn accolades and accolades will help your hubscore.