It depends on the length of your one-on-one classes, but present him with a series of questions based on a topic. Preferably choose a topic he's interested in, such as movies, music, travel, or something that will encourage him to give thought to the topic and questions before the private lesson. Then use the time in the private lesson to discuss these questions. This will help him develop fluency, as well as support his opinion. However, it's also important to take notes during each lesson so as to provide feedback in the last five or ten minutes. You can correct any mistakes, review grammar or vocabulary, and generally fine tune his ability.
As additional work, you can always ask him to research some information on the topic. Wikipedia is a great source because it's so readily accessible, and the student can research in his own language before browsing through the English information.
If the class is longer, say about one hour or more, then give him a short article connected with the topic. This can serve as a jumping off point to the discussion, and also allows him to reuse information from the article to substantiate his opinions.
I hope these ideas help.
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