Well, there are several things that you can try to attempt to lower your bounce rate, however bounce rate is not always as important of a metric as many make it out to be, especially on a site like hubpages.
A bounce is basically anyone that visits your hub, but does not click any other internal links(excluding ads.)
So, if someone finds you via google, reads the hubs, and clicks on one of your ads, this counts as a bounce.
If someone visits your hub, finds the information they need, and closes their browser, this counts as a bounce.
If, on the other hand, someone visits your hub, then clicks on one of your "related hub" links, this would NOT count as a bounce.
As a result, having a high bounce rate is not necessarily a bad thing and in many regards is to be expected on these types of sites. However, with that said, bounce rate is much more important metric on an e-Commerce site.
Many of the things that you could do to attempt to get a lower bounce rate, such as adding more links to your other hubs, would also mean potentially driving traffic away from your ads.
Instead, I would focus on trying to increase your ad click-through-rate and not get too hung up on bounce rate.