Usually we are inspired by what we basically know and see in your minds eye, then it what we feel, and then imagination takes over with what is occurring. 

Watercolour by Ada Fagan:

Caption title: Peaceful silver autumn wondering brooklet. 

This was a gallery demo I did some years ago.

People were requesting a serene autumn scene and this is what I came up with, as they watched me paint it. 

How to get your imagination running when doing demos:

Once you know the topic and type of scene that was requested: 

• Set a colour scheme in your mind. 
• Then decide on the mood. 

And with those two factors in mind, decide on the method of painting. 

• Whether to start with burred overall approach and then build it up with darker colours. 
• Or working section by section, working from the top downwards for landscapes. 

In this case:

I started by finely spraying the paper with water, both sides. That reduces cockle counterpoise buckling. And with the paper wet, it will create soft burring. 

• Then as you work, the paper starts to dry. And that means with each stage of dryness you brushstrokes will have more and more definition. 

So I started with the soft background and added more detail here and there, as the paper dried, where needed to complete the painting.