Find grammar and vocabulary resources online. There are many vocabulary and grammar resources available to students online that can help them to learn basic English. For example, LearnEnglish.de has many exercises in grammar and British English vocabulary, as well as a free magazine in English. Likewise, the British Council's Learn English website offers a variety of interactive ways to master the basics of this language.
Listen to English speaking materials. While some websites offer basic listening exercises for students of English, listening to what native speakers seek out can be an effective way to polish your language and move up to the next level. Websites like ABC (abc.com), NPR (npr.org) and BBC (bbc.co.uk) all offer podcasts--some in video form and others in streaming audio-- that will introduce you to a wide variety of accents and speaking speeds, helping you to understand and comprehend how native English speakers talk.
Read English language materials. The internet is full of excellent resources for reading in English. The first of these, newspapers are still free, for the most part, such as The New York Times (nytimes.com). If you have a Kindle or like to read books on your computer, Amazon offers many classic works of literature for free, or for extremely low prices. Also, reading a favorite novel in English can be an easy and enjoyable way to learn the language.
Connect with English-speakers. You can find English-speakers online who wish to learn Vietnamese and are willing to do a language exchange, by video messaging, instant messaging, telephone or email. Alternately, you can find teachers of English either in Vietnam or your current area who may be willing to teach remotely. If you do not wish to connect to an English speaker one-on-one, even reading forum posts and reading native English speakers' writing can help you adjust to the way in which native speakers use the language in everyday communications.