Prime your raw canvas with a black gesso. This will enable you to use the gesso as your foundation, instead of having to cover much of the canvas with darker colored paint--something that may be beneficial to some depending on the scene. Regardless of the color gesso you're using, you should apply three coats to your canvas before continuing onto composing your scene.
Decide the light source of the scene. Whether you're using a lamp or the moon and stars, every night scene will have a light source. The light source is imperative to the creation of the scene, as it will be the deciding factor of the temperature of the scene. Whereas the moon might create a cooler, blue, temperature, lamps and fire will create a warmer temperature.
Draw up a rough sketch of your scene, paying close attention to the design of your light source or sources. Determine whether your light sources will be warmer or cooler based on either their nature or your desired effect. If you're drawing up a night scene on the beach, chances are the temperature will be cooled by the moon and stars. That said, you could easily heat things up with the addition of a bonfire, which would demand warmer color, such as red and yellow. Let the temperature of your light sources determine what color you use and mark what color you plan to place where on the canvas--this will help you visualize how the color will mix with others.
Squeeze a fair amount of black paint onto your palette as well as a smaller portion of white--because you're creating a night scene, it's likely you'll be needing more dark than light shades of color. Use your palette knives to mix a little black with your primary blue. This will create a darker blue much like Phthalo Blue, which will help you create cooler temperatures to your shadows. Likewise, mixing a little black to brown or red will create a darker brown similar to Burnt Sienna, which can be used to add some heat to your darker areas. If you're combining both warm and cool light sources, you'll need to squeeze both browns and blues to your palette and mix them with the colors in your scene in order to create a blended scene with a clear sense of temperature.
Use your assortment of paintbrushes to apply the colors you desire for your scene. Blend the colors with each other as you paint to create a more naturalistic look to the scene. Amplify the temperature of your light source by adding either blue or brown to the shadowing areas around your light source.
Touch up your night scene as you see necessary. It's helpful to take a moment to observe what you have created as this will enable you to see what still needs work. Crush the darkest shadows by applying jet black and highlight the light sources by adding titanium white.