Below are helpful suggestions from the article referenced below for communicating more effectively with non-native English speakers.
1. Speak slowly, not loudly.
2. Use hand gestures.
3. Don’t use idioms!
4. Feel free to use incorrect English when appropriate.
5. Find different ways to say something.
6. Pronounce letters and phonemes clearly.
Source: Learn English Articles » Blog Archive » How to Talk to Non-Native English Speakers