Try using the different forms by thinking about different kings you know about, have read about, seen on TV. A mixture of English and Greek is fine, that's what you would have to do if you were able to go back in time and met an ancient Athenian. Wouldn't he be surprised!
There once lived a βασιλεύς in a faraway country. All the people loved τὸν βασιλέα because he was kind to all. One day, a peasant approaches (walks up to) προσχωρεῖ τῷ βασιλεῖ asking for the help of τοῦ βασιλέως  saying:
ὦ βασιλεῦ, ἵλαος, (or, 2nd edition: ἵλεως) ἴσθι  (lesson 2b, Dikaiopolis invoking Demeter to be gracious or propitious and multiply his seed)