One factor is understanding the reasons why the students have reading difficulties, while the other is finding some way to teach the subject content and reading at the same time.
Clary, L. M. (1977). The Why and a Little How--Teaching Reading in the Content Areas. Reading Horizons: A Journal of Literacy and Language Arts, 17 (3). Retrieved from https://scholarworks.wmich.edu/reading_horizons/vol17/iss3/10