1. Speak slowly, using simpler sentence structures--This does not mean talk to them as if they are stupid or use poor grammar, rather slow down (we Michiganders are especially fast!) and don't use compound sentences. Also remember that students cannot hear word beginnings and endings, you need to slow down so they can pick up on the pauses.
2. Longer wait times--This is especially important for your lower proficiency students. It takes time for them to listen to what you have said, run it over in their heads, search for words they know, think about words they don't, and then once they understand (or think they understand) what you've said, they have to go through the whole process again for their answer. In short? Take your normal wait time and double it, then double it again; and do that very difficult thing for us teachers and stay silent while they think.
3. Enunciate-- Language learners have to train their ears, as well as their tongues. Vowel sounds are especially difficult for them to hear. Think of an actor: they have to over enunciate to make their speech clear for large audiences, the same principle is helpful for ELs to hear syllables, multiple letters, vowels, and other idiosyncrasies of the language.
4. Repeat, repeat, repeat--As teachers we know the value of repetition. Research shows that it takes an average of ten meaningful encounters with a new word for us to truly learn it and be able to use it. This is a minimum for ELs and is increased for words that are challenging, such as homonyms, idioms, and abstract terms that may or may not have changed meaning through the years.
5. Visuals-- If you can visualize it, do it, and in as many contexts as possible. Pictures are key, it is not unusual for an EL to be completely lost with very easy vocabulary or concepts, but as soon as they see a picture to have a complete change and exclaim in their first language a translation or explanation. An easy way to increase visuals: add a picture to your word wall cards, don't just put a card on the wall that says "Acute Angle", put a picture of one too.
6. Kinesthetic Methods-- The more senses involved, the greater the learning, is teaching 101. This is magnified for ELs because the auditory methods and written text (often the foundation of our visual methods after kindergarten) are all but useless for them, especially in the beginning.
7. Turn on the subtitles-- Have more than one language in the room? The languages represented aren't included in the subtitle options? No problem, turn them on anyway. Seeing the words as they hear them helps students pick them up, it also helps with distinguishing where one word starts and another ends.
8. Read to them-- We know that all children benefit from being read to, research is now telling us that ELs not only need to be read to more than non-language learners, but as much as six times more! So break out those picture books, even for your older learners (they like them too, shhh--don't tell anyone).
9. Scaffold and scaffold again-- Prior knowledge is absolutely essential. An ideal lesson should present a new concept or new vocabulary, never both. If both are required the lesson will take much longer to properly convey, and may never be fully understood. The vast majority of ELs do have age-appropriate knowledge, they just need the English words to express it.
10. Love them-- OK, so this is obvious, the fact is that I really hate ending on an uneven number so I needed one more. The truth is that you won't find many students who are better behaved, harder working, or just generally amazing to have in your classroom than ELs. Just be careful, you may end up falling so much in love with them you find yourself back in school looking for a new certification. ;-)