Like everyone has already said, somehow I get to a Hub (or comment) and if it interests me, I check out the profile. If the profile is interesting, the Hubber writes about topics that interest me, I'll check out a few of their other Hubs. Then I decide if I want to follow or not.
I don't usually follow for a follow, but if someone starts to follow me, I at least check out their profiles and Hubs. I figure, if they are interested me, maybe we have common interests and I may also want to follow them.
Sometimes I run across a Hub or a comment that I don't agree with and I check out that Hubber. I have followed a few only because I feel it may be good to get a different perspective or opinion occasionally.
Finally, I try to follow quality. Hubbers that I feel (and often many others based on their accolades) are quality writers. I may also follow if I like the way they construct and present their Hub, use the capsules or photos, or have other techniques that I think make their Hubs look attractive or interesting. Some of the people I follow have over 1000 followers. I can only imagine what their daily HP notifications e-mail looks like!
The other side of the question is who don't I follow. If I read a Hub and it is poorly written, not well researched, or is overly short (shorter than this answer), then I won't follow. I also won't follow someone who has a Hub that sounds like it was just paraphrased from a newspaper article or some other source. I also don't follow if they are basically trying to promote their business versus use their expertise to educate me.
I also don't usually follow Hubbers with a lot of get rich quick or make money quick or easy Hubs. I don't think it works that way. Everyone is looking for the easy way. Almost everyone that has gotten rich, has done it the hard way with hard work.