While "content is king". in determining the potential revenue for a hub, There are a few more things that can really help.
Searching for the right key words and using those keywords in your hub is crucial. Just be careful and don't over-do (stuffing) otherwise you can be penalized by google for spamming.
Write an interesting and compelling title which will bring people to your hub. Also make sure your hub is at least 1.000 words.
Invite others to read your hubs by posting them on FB, twitter, Triond, Digg to name a few. Be involved in discussions and forums.
Sure it's a little work and time consuming, but if you perservere and keep on writing great hubs, the money will come!