Write clearly, whether you type or print. Make sure there are correct spaces between words and that you use correct margins. It can be difficult to look at a cluttered document even when someone reads English well, but if students are reading English as a second language, they need an especially clear document.
Check everything you write two or three times to make sure you are using correct grammar, spelling and punctuation. Even a small error that a native English speaker could easily understand can send ESL students into confusion. You will want to present them with a completely correct paper in each way possible, in order for it to be put to the best use.
Use language that is clear and concise. Do not use slang, run-on sentences or jargon. It is not necessary to dumb down what you are saying, but say what you would like to say in such a way that is very clear and basic. This will give your writing the best chance at being understood by those who do not speak English as a first language.