I think I can produce every individual phoneme in standard-ish spoken Mandarin.
However, if I want to speak fluently I have to watch videos of people speaking and closely watch their mouths, because mine isn't smart enough to put itself into an efficient shape for the next word.
I have resorted to drawing one word and then the next and then a figure showing the relative size of the mouth and arrows for its movement to remind me where my mouth should be.
# I use a diagram like this to remind me what shape my mouth should be in at a given word.
这 个 留 下
-- __ __
| | |__| o >--<
Is there a name for this sort of thing, or documentation for all the "mouth transitions" which a person has to make for a given language?