My EFL/TEFL students ask me the same question many times, and the answer that I give them is simple: Do not stop speaking it, listening to it, nor reading it. You literally have to live your regular life in the target language to be able to improve it.
See, if you are not a native English speaker, the best way to make your intonation to flow more naturally and your vocabulary to expand is by consistently using it. There is no way around it. You have to jump off the comfort zone of translation and jump straight into full immersion. Keep reading, speaking, and writing in English. That is all you need to do.