I select hubbers to follow based upon their writing, their topics, and their hubtivity. I also review who I am following every month to ensure I am still enjoying the person's work and want to be notified when they have new hubs posted.
On the flip side, if you want to know why we follow others, you may be interested in why we don't. I will not follow people who write articles with lowercase "i" and other grammatical mistakes consistently. I will not follow hubbers who appear to just blog versus post engaging and helpful content. I will not follow hubbers who are consistently posting rude and judgmental content in the forums. When I have followed such people and see this kind of activity, I have unfollowed them because I do not believe it supports the community spirit I enjoy so much here at HubPages.