Paint Shadows First
Buildings, trees and mountains don't move much during the day! But the light does! It is surprising how often a well lit scene captures your imagination and you decide to paint it because of the interplay between the sunlight and the shadows. But by the time you have sorted out your painting kit and got set up, the shadows have already moved a little, and you realise that you will have to paint very quickly indeed to capture the scene.
So why not paint the shadows first before they move? This may seem like a daunting proposition, as we are all so used to adding shadows on to our painting at the end when all the other parts have been carefully painted in. But with a little practice it is quite easy to see where the shadows are (just squint up your eyes a bit to se them more clearly) and what there size and relationship is to one another.
Then paint them in exactly as you see them.
Then finish the painting at your leisure!
Once the shadows are in, nothing else is going to move, so you can take your time and enjoy painting in the rest of the scene, as I did here with this jumble of old French houses.