Contextly's recommendation system looks at a number of features of your posts to decide which other posts it is related to. That includes the headline, author, tags, categories, and the content of the post itself.
If you want to change which features are more important, you can do so in the Control Panel. Instructions are below.
You may want to do this if you have very good tagging or if you have authors that readers have strong affinity for. In that case, you can make tags or authors more important.
Alternatively, if your tags and categories aren't good, you can make headlines or the body of text more important.
You can try this out and see the results in the Control Panel, under the Recommendations Tab, choosing Adjust Related.
Then you can use the sliders like an audio equalizer, and see how the results change on the right.
Don't forget to press Save when you like your new mix.