The Practice of English Language Teaching by Jeremy Harmer is for English teachers or those training to become English teachers. I am currently reading it, and I must say it is quite interesting. It's been recommended by several sources.
I advise reading it if your serious about Tefl teaching, I will move onto a grammer book next as my English can sometimes leave alot to be desired!
Anyway, if your about to or already in the teacher training process this book is a must.
The Practice of English Language...

This third edition has been completely rewritten and updated to combine the best of traditional approaches with the latest developments in language teaching theory and methodology. Offering a comprehensive and up-to-date account of theories of language and language teaching, the guide includes a wide range of practical teaching ideas, example lessons and samples from current teaching materials. It also focuses on the sociological and psychological perspectives of language and language learning.

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