To people who want to learn German I recommend the following books with which I work with my students already a lot of years:
1.) „Begegnungen. Deutsch als Fremdsprache / Integriertes Kurs-und Arbeitsbuch“ (title of the book; engl.: Meetings. German as foreign language / integrated lesson and work book)
Authors: Anne Buscha & Szilvia Szita
Publishing house: Schubert Verlag (in Leipzig)
I recommend this book because it provides a interactive learning between teacher and student. It leads the student to an autonomous learning of this language. The goal is that German learning people come along with German in the different speaking situations without the teacher.
Further advantages of „Begegnungen“:
The student learns a correct and sophisticated German:
German has a lot of similiarities with latin. For example the nouns in the German language are declinated like in latin and German shares its specific logic. „Begegnungen“ pays a lot of attention to this fact. The students learn also the logic of the sentence structures.
For German teachers:
There is also separate book, a teacher hand book (Lehrerhandbuch) that refers to „Begegnungen“ with additional exercises that the teacher can do with the students who work and learn with „Begegnungen“.
2.) „German DeMystified. Hard stuff made easy “ (title in German: „Deutsch Entmystifiziert)
Author: Ed Swick.
Publishing house: Mc Graw Hill“ (USA), 2nd edition.
The advantage of this book is that it is written completely in English, so English speaking people get the whole explanation of the German gramar in their native language.
I recommend this course book for English native speakers who want to learn German slowly and comfortably.