RPD (Relaxed Pronunciation Dictation) is a simple but effective listening exercise to get your students’ ears used to English as it is naturally spoken by (some) native speakers.
Although I tend to favor a top-down approach to teaching English, I have found this bottom-up exercise to be very helpful in developing my students’ listening skills.

Here’s how to do it:
Choose one of the examples from the PDF (or make up one of your own) and repeat it several times while your students write down whatever words they can catch. You may want to slow your speech down a bit, but try not to make it clearer. The whole point is for the students to get used to the phonetic shifts that result in utterances such as “Jeet yet?” (“Did you eat yet?”) You may also want to give, as a hint, a context in which the utterance might be used.

After several iterations of the sentence, I draw blanks on the board—one blank for each word—to show how many words are in the sentence.
Then I like to elicit one word per student at a time, so everyone has a chance to contribute to the solution.
Once it is all on the board for all to see, I first make sure everyone understands the sentence—grammar and vocabulary. Then I show the students what is happening with the phonetic changes.

For more information about the phonetic shifts I am talking about, consult a resource that addresses these issues. I learned most of what I know from Sound Advantage, by Stacy Hagen and Patricia Grogan (1992, Prentice Hall, ISBN 0-13-816190-9), and Sound Advice, by Stacy Hagen (2000, Longman, ISBN 0-13-081361-3).

Here’s the link to the PDF again:  Relaxed Pronunciation Dictations PDF