Look for local English classes in your area. Speak to your local British Consulate or British Council office if you cannot find these classes, as they will be able to give you advice.
Read English-language websites on the Internet. Websites such as the BBC mix video and text, which will help you improve your formal English, as well as get an idea of what makes the British culture.
Find someone to converse with in English. Ideally, this person should be a native English speaker. If you have a friend who is also practicing the language, you can spend an hour speaking only in English to one another. Find someone who is learning Cantonese and offer to chat for half the time in English and half the time in Cantonese.
Watch English-language shows to gain an appreciation of how informal English is spoken. Watch your favorite shows in English to make the exercise more enjoyable. Watch DVDs of films in original English to ensure that you are not learning English from mistranslations.
Go to an English-speaking country. There is no substitute for immersing yourself in English-speaking countries to improve your language. Spending time in the UK, the US or Australia will force you to speak English all the time, which will ensure a rapid improvement in your language abilities. This is the best method of learning English.