Laissez-moi vous raconter une histoire
When I introduce myself and say a little bit about myself, recounting the exciting story of my life thus far (in which I am the star), I can sound relatively fluent in French. On those occasions I lap any compliments which are forthcoming (genuine or not) to nourish my confidence.
However, this relative fluency is due to two factors. Firstly, I will have practised this introductory speech many times. Secondly, I am talking about myself which is really my specialist subject. The difficulties come when I am required to go beyond this well-rehearsed comfort zone and deal with unexpected, improvised subject matter.
Approfondir le discours
You can use your French discours to experiment with using more complex and varied French expressions. If you can incorporate them into your more frequently used monologues, you will remember them and have a personalised context in which to employ them. The idea is that later on you find yourself using them more spontaneously.
One idea might be to maintain and update written accounts of common conversational topics such as your job, your hobbies, your french language learning experiences, your life story (abridged version) and your ambitions. Every so often you can upgrade and spice up your standard routines with new more sophisticated phrases!