There is a very simple way to improve your Adsense targeting, and it is called section targeting. There is no trick behind this technique, and Google itself incentive users to use it, here is a quote from the Adsense Help Center:
Section targeting allows you to suggest sections of your text and HTML content that you’d like us to emphasize or downplay when matching ads to your site’s content. By providing us with your suggestions, you can assist us in improving your ad targeting. We recommend that only those familiar with HTML attempt to implement section targeting.So how do you implement section targeting? All you need to do is to place the following tags before and after the content that you want to get targeted:
Content to be targeted here
You can use as many sections as you want inside your page, and you can also place them on the header of your page so that meta keywords will be included. Bear in mind that it might take up to two weeks before you see the results of the section targeting.