Today I had a student ask me how they can increase their vocabulary, because this person feels that they use only very basic words and have a child's vocabulary level in English. So here is the answer I gave:
It is perfectly normal to have a limited vocabulary as an English learner, especially when speaking. Even we native speakers usually save our advanced vocabulary for writing. We tend to be informal and casual in conversation. But you still want to sound intelligent, I know, so yes, you'll want to expand your vocabulary.
You need to understand that your brain is designed to only remember important information that will help you survive. So if you are trying to remember a lot of random words that you don't really need or use every day, your brain will immediately forget them. You have to convince your brain that these words are needed and useful. If you learn a new word, and then you hear it on an English-language TV show, and then you use it in an email to an English-speaking company, and then you use it in a recording that is homework for your English course, and then you use it in a conversation with an English-speaking friend, are you going to forget that word? Of course not. You have proven to your brain that the word is needed and useful to you. So keep this in mind during your studying. Memorizing lists of words does not work. It is more helpful to discover new words by interacting with English. If you are trying to write an email to me and you need a certain word, and you look it up and use it, you are more likely to remember it. Try to express yourself in English as much as you can. Look for as many opportunities to do so as you can--take a class, join online groups, etc. And watch a lot of English-language TV and English learning videos, and listen to English podcasts. Read news and other articles in English. Add in new words little by little that you hear or read in these environments. And your vocabulary will expand. You will also be more likely to use the words correctly because you will also have picked up the context that the word is used in.
Remember that language learning is slow. Keep practicing and be patient with yourself, and it will get better over time, I promise!