HubKarma means very little as far as I know, it's just a number on HubPages. I must say I don't spend much time promoting my hubs but from what I can see the goal of promoting is to get inbound links on other websites.
The quality of the links also matters: are they genuine and are they really part of the content of the webpage or just at the side, things like that. I can't really give you specific advice on promoting hubs but I do know that it's a personal preference. Some spend a lot of time on it while others focus on writing high quality content with little to no time on promoting (while still doing well moneywise).