
Recently, there has been a lot of attention paid to painting nocurnes, and why not?
They are very visually appealing, and although a challenge, a LOT of fun to paint.
Many terriffic artists have also written blog posts, magazine articles, and have done u-tube videos on the subject. I'd like to throw my two cents in, as I have been painting them on and off for about 25 years now. My approach may be a little different, in that I do not use a miner's lamp, or attach lighting to my easel, which is what is used most often for painting one from life.
I have painted them en plein air, from memory, and also studio versions from photo reference.
My very first ones were in watercolor.
This is one from a large series I had done from the shores of the Hudson River. I would pick a spot around dusk, and start painting as the lights were just starting to twinkle on. Many were right from my car, so that as it got much darker, I could turn the overhead dome light on and off as needed. It was photographed under glass, so there are extra twinkles.

" Harvest Moon Memory" is just that, a piece painted from intense , focused study of the subject, which I observed on my way home from dinner with a friend. The next morning, I painted it from memory, making sure to keep my values very close together. My working knowledge of having painted numerous orchards from life helped in this one.
"Casa Twinkles", 16x20 was painted on location, over a period of 2 evenings, as it is a subject that is a bit more complicated. I set my easel up on a corner just after the sun had set, and I had enough light to get started. Since it is pastel, I think it is necessary to be able to see the sticks, select out the ones that will be used, and keep them out. As it gets darker, it would be virtually impossible to pick them out from a full box of color. I roughly blocked in the shapes on the first evening, as well as painted the figures. The following evening, I was able to refine some of the architectural details, and add the lights.

"Moon Over Cottonwood" was painted en plein air, as well. I observed the moon rising the night before, which was spectacular. So, I made mental notes as to where it would be coming up the following evening. So, at that time, I set out my easel, and blocked in the darker vegetation and horizontal planes, anticipating the moon rise. This is an oil, so I pre mixed colors, and laid in the big shapes. I had observed that the area around the moon would be warmer, so that is how I painted the sky in that part, before the moon came up. When it did, I was ready!
"Blue Moon", pastel is a studio piece, done from photo references. Again, a moon rise, and a classic car on a side street. When painting cars, or architecture it is important to get the proportions and perspective right. Also, being in studio allowed me to play with color, in that I kept the palette very cool and blue. I exagerrated the setting sun's reflection in the car's rear window, which adds a warm note.
So, my tips for painting nocturnes are:
Remember to keep your values close together.
Most color will be greyed.
Observe, observe, observe from life, as much as possible, making mental notes when you can't get out to paint the night.
Edges will be soft, and indistinct.
Try setting up just after sunset, while there is still enough light to see your palette. Paint the sky, and other big shapes, quickly. Lights that come on can then be added. Be mindful not to paint the lights too bright or light.
It would also be good to paint small works, one right after another.
Know your palette colors, or pastel sticks.
Beautiful effects that occur during low light are just waiting to be captured, so go for it!