One of the best methods to expand your vocabulary knowledge is to read a lot and apply your knowledge by writing.
You can also use flashcards to back up your learning.
Read across a broad spectrum of topics, and read into them deeply. Don’t be afraid to read unusual topics if that is what interests you.
Keep an eye out for words and phrases that catch your attention. Pay close attention to how those words and phrases are used in combination to get the point across in an engaging way.
Read the daily newspaper and pay particular attention to the political and economic news – don’t just skip ahead to the cartoons and sports section! The political and economic topics tend to be written by experts in the English language, and will therefore make you sound more and more like an expert too.
Watch films in an active way. Of course you can sit back and enjoy the story first and foremost, but keep listening for interesting words and phrases that the characters say. They will often speak in a very natural, native way too, so listen to the way they speak.
Keep a notebook on your person at all times, ready to jot down any new vocabulary you come across in the course of your daily life.
Write as much as you can. This doesn’t mean you need to write a whole novel; start out by writing some internet comments, write down your thoughts in an English diary, and find some penpals. This will also train your grammar as well as your vocabulary.
Try to apply the vocabulary you have learnt in real-life situations. Keep new phrases firmly in your head and never miss an opportunity to sprinkle them into your conversations, your work meetings, presentations, or any other oral activity.
To expand your vocabulary quickly without much extra effort, write down synonyms (words with the same meaning), antonyms (words that mean the opposite), and variations on the word using affixes. For example, “comfort” can be expanded to “comfortable” and “uncomfortable”.
Once you’ve mastered some vocabulary, you can begin making your own sentence constructions.
It’s also worth writing a copy of the sentence from which you learnt the new vocabulary. This will reinforce the words much more effectively than simply looking at it, and it will also help you remember where you learnt the word in the first place.
When you see the same word again in another context, make a note of the new context you find the word in. This way you will build up a full picture of how the word can be applied in real life.
If you categorise your words by theme, this may also help to organise your thoughts.
This might all look like hard work. However, it is definitely worth doing because the process of seeking out new units of vocab and multiplying them using word variations will give you a rapidly expanding and interlinked collection of vocabulary.
In summary, the real test of your increasingly bountiful vocabulary will come using it and consistent applying in your daily life. Taking part in real-life communication with real people, as much as possible, in order to reinforce your practical skills and memory retention and recall.