Hi Tom,

I notice your level is already C1 which is what we used to call 'advanced', so the next level is going to be a slow process. 

I would recommend reading newspapers and books, listening to French radio or watching French programmes on the television would help to improve your understanding and build up your vocabulary but to improve your fluency, you need to go and live in France for a bit.

Here are some notes and the CEFR  levels -

CEFR - The Common European Framework of Reference for Languages for Learning, Teaching, Assessment