If you really want to build your English vocabulary, why not try to learn at least one new word every day?
I will be posting a "Word of the Day" on my Social Media, so if you follow me, you'll be able to achieve this goal without too much effort.
The wider your English vocabulary, the more confident and fluent you will become. Remember, it's important to understand the meaning of the word so that you use it correctly. When you write it into your vocabulary book, write some example sentences, any synonyms that you can find, the definition in English and the translation into your own language. You can even add a picture if that helps you to remember!