Just lots of practice all the brush strokes over any perfect leaves/stems. 
I used the different mix of 3 primary colours, ultramarine blue with black, yellow ochre wirh rose madder, yellow ochre with ultramarine blue and yellow ochre. Experimented to have autumn 🍂 colours and blue/greens 🍃 
I always love Nicki's muted colours in her work. 
Thank you Nicki, for your lovely class 🧡