This report from Education Northwest outlines 14 key principles that will help guide classroom and content-area teachers in their planning for ELL instruction and provides instructional implications for each principle. While it was originally written for lawmakers, it is a user-friendly overview that can be used in school or pre-service settings.
Deussen, T., Autio, E., Miller, B. Lockwood, A.T., Stewart, V. (2008). What Teachers Should Know About Instruction for ELLs. Education Northwest.