Choose a class designed for business English. English conversation schools have different focuses for their classes. Some are meant to help people learn English for traveling, while others are meant for business speakers. You need to be sure that you choose the business style of classes at a level that is challenging for you. Most schools will offer a test to help place you into the right course, and you may be able to get a free lesson to determine if you like the school.
Use a business English text book. If you're studying on your own or with a private tutor, it's important to use a text book that focuses on business English. For example, the "Market Leader" series is a good choice because it offers text books from the elementary to advanced levels. "Business Vocabulary in Use" also has different levels.
Listen to business English podcasts. Listening to English on a regular basis will dramatically improve your conversational skills. You can download sample business English conversations and listen to them in your spare time. The BBC even offers scripts of their conversations to help you learn. Repeat the phrases as you hear them so that you become used to forming the words out loud.
Take the TOEIC test. The Test of English for International Communication is the standard test when it comes to business English. Scores range from 10 to 990 and the highest level that you can achieve is the gold level, with a score between 860 and 990. You can use this as a measure of your English level.
Practice as often as possible. The only way to truly become fluent in a language is to do your best to speak the language. Take every opportunity that you can to speak the language. You can do role plays in your English class, and you can also volunteer to be the English speaking contact at your office. While things may be difficult at first, you'll find that you become more and more fluent.
Learn new vocabulary by reading business news. Turn to English publications, such as the Wall Street Journal to improve your English. You should also read publications that are specific to your industry.