Here are some of the teaching materials I use for my German lessons.
I highly recommend the textbook called "Deutsch Heute". You can choose any of the versions and editions, click HERE or on the image below for the edition from 2015:
Pretty obvious study aid, but I always recommend flash cards for vocabulary and memorization. You can make your own, or just buy a set of 100 cards for only a few bucks:
I recommend a few external websites to my students and use elements of them in my teaching for grammar, vocabulary, sentence structure, etc:
German cases:
More on German cases:
And finally, if you are struggling to type those pesky German Umlaute on your American keyboard, this website may be a great help to you: