Well, it depends. If your hubs are really popular and they rankk well in search engines, then you have chances to get AdSense clicks and Amazon/eBay sales. If you've signed up for HubPages ads and impressions program, then you'll be getting money for just impressions. If you hub receives traffic, then you get money.
To maximize your chances of making more money, write on commercial topics like Health and Finance. Make money online is a good topic too. Anyways, it ultimately depends upon your writing, traffic and commercial appeal of your hubs. If you can write engaging hubs which attract a lot of comments and followers, then you'll be making easy money via HP ads.
Focus on creating backlinks to your hubs and promote them via Facebook and Twitter. The more traffic your hubs get, the more money you make.