In Modal verbs^x, TEFL^x

Practical English Usage by Swan, publ. Oxford is very good. Emphasis, however, is upon proper English, rather than the American version. Alternatively, use the web, for example http://www.englishpage.com/index.html and http://www.ucl.ac.uk/internet-grammar/home.htm

friends, i'll shortly be taking a TEFL course and then continuing on to work as a teacher and would like to familiarize myself with the basic rules/issues before leaving (i don't leave for months) and am soliciting recommendations for books that explicitly deal with the issues I'll be...