You will find many wonderful – and free! – teaching materials online. The internet will likely be one of your primary sources of teaching materials. However, there are a few resources which you may wish to purchase. Why would you purchase materials, when there is so much free content out there? The main reasons are the quality of the lesson materials and the time savings to you as the teacher.
Obviously, you’ll want to use good-quality materials in your class, and everything I suggest on this page qualifies. These materials are effective and professional-looking teaching tools. I personally use everything you see below.
In addition, using pre-done materials will save you TONS of time when you sit down to do lesson planning for the coming week. As your teaching calendar fills up, you’ll appreciate more and more being able to simply send a student a link or a PDF, rather than ahving to create a lesson about the present perfect from scratch.
Whenever possible, purchase materials in digital format, so that they can be more easily shared with your students. Otherwise, you’ll need to scan in paper materials first. Alternatively, your student could buy the same material.
GRAMMAR
Cambridge University Press produces a great series of grammar texts. In each, lessons are brief and focused, with the lesson itself on the lefthand page, and exercises on the right. More complex topics are subdivided to confirm to this two-page-per-lesson format.
There are three books in the series: Essential Grammar in Use (basic level, red cover), English Grammar in Use (intermediate level, blue cover), and Advanced Grammar in Use (green cover). I recommend buying the basic and intermediate books; I find that I rarely use the advanced text. You may wish to have your students also buy the baisc or intermediate text, according to their respective levels.
Note that some texts come with answers to the exercises and a CD, while others do not. I suggest spending a tad more to get editions with answers and CDs.
COURSES AND PRE-DONE LESSON PLANS
I’ve looked at numerous providers of pre-done lessons. Two which I like and use a lot are ESL Library and Espresso English.
For beginners through intermediate-level students, ESL Library is a good choice. Among other things they offer many scenario-focused dialogs, such as “Going to a doctor,” and lots of grammar worksheets for practice. But they also have lots of discussion-centered lessons as well. They are a subscription service, but very reasonably priced, and they are always adding new materials. I believe they currently charge $33 per quarter, and you can cancel at any time.
For intermediate to advanced students, my absolute favorite materials are from Espresso English, the brainchild of an American woman named Shayna Oliveira. She offers courses on pronunciation, phrasal verbs, vocabulary building, business English, and more. I bought everything she offers (and received a discount of 35%). There is not a week, hardly even a teaching day that goes by, that I don’t use some Espresso materials. I encourage you to take a small portion of the money you saved by not getting a TEFL or CELTA certification, and invest it in Espresso materials.
There are many other companies which offer prepared lessons. LinguaHouse is another big name, and I used them for awhile, but frankly I didn’t care for them as much as ESL Library or Espresso. But they’re OK, and they offer many lessons for business English. They also are available by subscription, I think only about $50 per year, so you could certainly try them out.
IDIOMS AND PHRASAL VERBS
Students love to learn idioms (expressions). Learning idioms is fun, and moves students to the next level in their study of English – like being admitted past the velvet rope.
Phrasal verbs bedevil students of English. For those of you who may not be certain what a phrasal verb is, these are two- and three-word verb constructions formed by adding a preposition or an adverb (or both) to a verb. Examples include: get off, get into, get out of, put off, and put up with. Imagine trying to eexplain why “put up with” means “tolerate”! You’ll need a good resource or two.
Teacher and author Amy Gillette has written a series of books which teach commonly-used idioms and phrasal verbs in a fun way. I use them with most of my students.
Speak English Like an American teaches common idioms through a continuing story about Bob Johnson and his family. Each 
lesson is a dialogue of a page or so, wth idioms in bold type. After the dialogue, idioms are defined and additional examples of usage are provided. Each lesson also contains a quiz, and there is a review every five lessons. Each lesson requires 15-20 minutes. Very enjoyable!
More Speak English Like an American is organized in the same way as the first book. The continuing story follows employees of a food company as they create a new product line and even travel to China.
Speak Business English Like an American is organized just a bit differently in that there is no continuing story. Each lesson is instead devoted to learning idioms pertaining to a particular aspect of business. One lesson relates, for example, to project management, another to launching a project, and another to marketing. You and your student can pick and choose the lessons of greatest interest or relevance. Gillette has also written another book specifically for those in business, Speak Better business English.
All of Gillette’s books are available on Amazon.
WRITING
If you may be teaching writing, I suggest picking up a copy of The Little Red Writing Book – yeah, cute, I know – by Brandon Royal. It should only be a few dollars on Amazon. It’s concise and very, very good, emphasizing construction, but also discussing style and common grammar mistakes.
I can recommend all of the materials on this page. If you purchase them, and then augment them with online articles and materials from free EFL websites, of which there are tons, then you have most of what you’ll need to construct really good lessons.
You don’t need a lot of materials, just good materials.