HubKarma is mostly based upon how much your Hub(s) link to other Hubs, as related to the keywords selected. The Link Suggestion Tool is very helpful for this.
You can link to other Hubs that you have created.
I believe that the amount of external traffic plays a huge role, as well as time spent on the page. Also, how many clickouts are done, possibly giving emphasis to Ad clicks and clickthroughs to other Hubs or external links.
HubPages does not share the ratio or algorithm with us, so you kind of have to guess.
For reference, here is what HubPages tells us: "HubKarma is a score that reflects the degree to which you link to others' Hubs and to Topic pages in your own Hubs. Hubs that point to other relevant, high quality Hubs enhance readers' experience on HubPages and improve HubPages credibility as a trusted resource. HubKarma has some influence on your Hubber Score and is on a 0-100 scale. The link suggestion tool makes linking to other Hubs and Topic pages easier." - http://hubpages.com/faq/#hubkarma