Ways to improve your intonation
The best way to improve your intonation is simply to become more aware of it. By listening carefully to a recorded conversation (YouTube is a good place to start), you will begin noticing how other speakers use intonation to express themselves.
Another idea is to record your own voice. These days, even the simplest mobile phones are equipped with a voice recorder. It is always fascinating (though sometimes unbearable) to listen to one's own voice because it sounds so different to what we expect! Try recording a dialogue with a friend, (you could use a script from a course book or scene from a film). Now listen to your intonation. Does it sound natural? Does it express your attitude in the way you hoped?
With a recording, you can always rewind, listen again and try a new version. Recordings are an excellent way to keep track of your progress. They clearly show how you have improved over time.