How do you widen your vocab in french?

Answer 1

I would advise to read. Choose authors you like and enjoyable stories, but not too hard as you will grow weary of the effort. You can find English authors, translated in French if you like, and the translations are usually very good.
I look for the new vocabulary, up in the dictionary. Most of these new words will not become part of your active vocabulary (the words you use) but only of your passive vocabulary (words you understand without looking any more at their definition, when you come across them later)

For advanced learners, you can try using a French/French dictionary. That will give you an understanding of the word, but also alternative ways of expressing yourself.