Have a variety of courses suited to your abilities
Chances are that you are wanting to learn English quickly, so for this reason your course needs to be enjoyable and suitable to your current abilities. The amount of time you have to study will depend on your other commitments to such as work, childcare and sporting commitments, so having a range of courses lengths to choose from is a bonus.

Meet other students who are in a similar position to you
Utilizing the skills you learn with others who speak English as a second language, is a great way to check your progress and understanding of the language. Not only that but if you are enrolling at a school which is away from your home country, it's nice to have someone to share experiences with and make friendships.

Get a dedicated ESOL teacher
Having experts who are qualified to teach the English language ensures that you are getting a quality learning experience. Also, qualified teachers are more likely to keep up to date with new approaches and resources too. Having a supportive learning environment is very important when you are outside of your comfort zone.

Clear curriculum goals
Not having clear goals about how long your course is going to take or what the learning objectives are can be a hindrance to your education. An English as a second language school will have their courses well organized into weekly modules and will clearly explain the goals and aims of the curriculum.

Personalized teaching & progress monitoring
Enrolling at an English as a second language school will most likely require you to undergo an entry test and interview where you will be tested for your current language skills. This enables the school to cater your learning format to your abilities and provide recommendations and guidance along the way.

All of the above points are important to your learning of the English language and being able to use it effectively. There are plenty of courses online for you to sign up to and use, however amongst other things you don't get the benefits above and therefore may not be getting value for money.

Source: http://EzineArticles.com/?expert=Kris-Helena_Ngau_Chun