I've been able to speak English quite fluently for a while, but I never stop learning. I encounter new words every day.

Here's a simple routine I use for that :

- just write down new words or expressions you learn as you encounter them

- make some Anki flashcards out of it

- review everyday

The words I discover are not words I would see every day, because they're very specific. That's why I think such a routine is essential for my level.