I took a quick look at a random hub of yours, "How to Hit a Backhand". The Hub looks nice (maybe "too" nice and informative), but I saw only a couple of ads, and they were only in the right sidebar, and even worse, the ads were about golf, not tennis.
No ads at top of your text, nor any in or next to the first few paragraphs. Make sure your Hubs are enabled to show the maximum number of ads, and experiment with text module size and other modules to get the ads to show where they need to.
Also, ten Hubs is a good start, but not nearly enough. You need many more Hubs, targeting keywords that people actually are searching for, not just what you think is a good idea. Then when they get to your Hubs, they will need to click on the ads in your Hubs to REALLY find out what they're looking for. You want them to go away by clicking on an ad, not going to another Hub.
Search for "SEO" and "keywords" and "Google Adwords Keyword Tool" here or on the web.