but first you want to assess their English level. Most likely you will have students on various language levels from beginning to advanced. I am attaching a modifications checklist and an example of a modified summary of one lesson in my SS text. I use lots of pictures, collaborative activities, differntiation, etc. I have come to learn that teaching ESL is really no different from teaching any other struggling student. A lot of the strategies are very similiar.
When modifying just keep in mind that you need to keep the language as simple as needed but keep the content expectations high.