Any of us who have ever had ELs in class have likely noticed that while many of them speak and understand English well, they struggle to read and understand texts. This is normal; all of us, when we were children, understood language first, then were able to speak it, and then we learned how to read and write. This was partially due to developing from a baby into a child, but also because that's just how language is acquired. Therefore, ELs specifically need focused instruction on academic language: words that mostly appear in writing such as articles and textbooks.
The CCSS divide words into three tiers: tier 1 are everyday words that most students learn in elementary school. They don't usually cause a problem for native-English-speaking students, but some ELs, depending on their proficiency, may have trouble with them. Tier 2 words are words that are more commonly in written text, such as formulate, itemize, periphery, faltered, saunter, etc. These are the words that I'm going to focus on in this email, as both our ELs and native-English-speaking students often struggle with them. Finally, tier 3 words are domain-specific. Here is one list of common tier 2 words.
A good place to start with vocabulary instruction is Robert Marzano's six-step progress for vocabulary instruction. The steps are as follows:
For steps two and three, I often use a "Four-Word Sheet." I attached the one I made. You could also use this for native-English-speaking students; just take off the "word in your language" line.
For step 4, you could use a variety of activities. I've used word clouds in the past, but a site I recently learned about is Word Sift. You copy and paste any text into it, and then it provides an abundance of information! You can make a variety of styles of word clouds, it gives text information (such as readability and unique words), you can sort words from rare to common, mark words that are on word lists, and more! You could use this site in a bunch of different ways.
You could make a word chart of important tier 2 words from an article or chapter and have students define/use in a sentence/draw a picture, similar to the 4 Word Sheet. Or you could have students choose the important words for their word charts! More oldies-but-goodies are word webs or cloze activities (fill in the blank).
The New York Times also has a lot of good resources for vocabulary instruction. For example, their "Word of the Day" feature has a different tier 2 word every day with the definition, use in context (including how many articles it's been in in the Times!), and a quiz to see if you understand it. You can also have students search for a specific tier 2 word to see how many article it's in and how it's used in each.
I hope you find some of these suggestions and strategies useful in your classes!