1. Ask how many students are in the class
In my experience of being an English teacher, the more students there are in a class the more difficult it is to progress. The smaller the class size, the better. I would recommend that if there is fifteen or more students in a class, don't do the class.
2. Listen to recommendations
Speak to people you both know and trust for their recommendations for English classes, courses or academies. You can also search for 'reviews' of online courses and language schools/academies on google/bing. But be careful with online reviews, they can often be written by the course/school themselves or by their competition.
3. Don't do courses which promise you'll speak or improve your English very quickly:
Don't do courses which promise that you'll speak perfect English in 100 days, it's not possible I'm afraid. Learning a language is difficult and takes time. Any online course or language school/academy that says they can teach you perfect English in a year is lying and should not be used.
4. Learning English isn't cheap
Like with most things in life 'you get what you pay for'. This means that if an English course is very cheap, the quality of the product or course will probably not be very good.
There are ways to save money when paying for English classes/courses. Many English language schools/academies and online English courses sometimes give discounts or offers. Look around and see what offers/discounts you can find. Also, online classes/courses with a teacher are normally cheaper than classes/courses in language schools/academies.
5. Online classes or language schools/academies?
In my experience both English classes/courses online and in a language school/academy can be very good. In the past, online English courses/classes used to be terrible, but now with better technology they can be very good.
The decision of which to choose depends on you and your available time. If you work or travel a lot, it is probably best to choose online classes. With online classes you can choose where and when you study. They are also normally cheaper than courses at language schools/academies.
If you choose online classes, make sure that the price you pay includes one-to-one sessions and/or direct contact with teachers (so, you can ask them about any doubts/questions you have).
6. Native or non-native teachers?
Some students think that a native English speaking teacher (from Britain, USA etc...) is better than a non-native teacher (from Spain, Japan etc...). In my experience as a (native) teacher this is not true. I have known some terrible native teachers and some excellent non-native teachers.
One of the advantage of having a non-native teacher is that they have experience of learning English themselves and understand the difficulties people have. This is good for teaching students with a low level of English (below intermediate)
But if you already have a good level of English (upper-intermediate or above), a native teacher would be the best option for you. They will help you improve your pronunciation and you'll learn more advanced vocabulary (expressions, phrasal verbs etc...) from them than you could from a non-native teacher.
7. Choose classes/courses that focus on speaking, not on grammar
In the past, most English language classes/courses focused on teaching English grammar. Although learning grammar is important, knowing the rules isn't as important as actually using English. You should look for classes/courses where speaking and listening are important parts of the class/course.
Before you decide to choose an English course look at the the course's programme and see if the course/class is focused on using English or learning grammar.
8. What to expect from the course and teacher
The purpose of a good English teacher or course is to help you, nothing else. Showing you where you are making mistakes, explaining things to you, answering your questions/doubts and letting you practise. Although this will help you improve or learn English more quickly than you could by doing it yourself, you will still have to study and practise outside of class.
If you don't do this, you will be disappointed with the progress of your English. So read, listen, write and speak English whenever you can outside of class.
Click here to see advice on how to improve your English
