YOU can't increase CTR. You can do what you can to try to keep your ads relevant, but pretty much anything you might try to increase CTR would be outside of AdSense TOS.
I don't know what kind of entertainment site you have, but think about user intent - are they coming to your site while they're in a buying cycle of some kind? If not, then you're probably never going to have a really good CTR. The best performing AdSense sites are going to be the ones that match up closely with people who are in the market for something.
The ones that just have clicks as a kind of "by the way" next to informational content (and most of my sites are like this too) are never going to perform as well.