Keep in mind:
- Internalize the rhythm of this pattern before you play it. Try saying the rhythm of the entire pattern out loud - "down up down up down up down up down up down up... up down up". If you can't say the rhythm properly aloud, you won't be able to play it.
- It is very important not to pause between the two strumming patterns. Listen to the audio file, and note that there are no pauses when the pattern switches, and no pauses when the exercise repeats.
- Try playing the exercise alone, as slowly as slowly as necessary, as long as the rhythm is correct (no overly long gaps between patterns, etc). Eventually, you can try playing along with the audio example.