Remove "clutter" and visually open the space
There isn't one "look" for a calm decor but there are guidelines/principles that can help you achieve a quieter environment in your own home.
Minimalism and Zen come to mind immediately when you use the words serene and calm because both aesthetics translate into living with less of everything- colour, objects, furniture, etc. It's about selected focus and getting rid of what is meaningless. Ask yourself what is absolutely essential and remove the rest. It's liberating! Rather than a gallery wall of art use one well chosen piece as the hallmark of the space. Rather than 8 pieces of furniture perhaps 4 will suffice. Put thought into what you want to display.
A clutter free home is usually achieved by having a place for everything and that means adequate behind the scenes storage. Of course filling up drawers and cabinets with junk defeats the purpose! Purge to the core.
If you want a calm look you have to think about colours that are soothing. It won't be red or orange! White is at the top of the list, but if that is too stark, go for other restrained colours like soft grays, ivories, soft beiges and neutrals that hint at lavender, green or blue. Consider painting walls and trim the same colour. Then add accents that are softer colours like this beautiful green.
Choose bursts of colour in smaller accessories like pillows or vases. Hang one colourful artwork or stack objects on a tray. Again less is more. Note how the light textured rug helps to soften the harder lines of the furniture.
Simplify window treatments or have bare windows
Keep it simple, consider textured glass inserts or translucent film rather than draperies. If you like the softness of fabrics go for very clean lines and soft colours. Natural fibers translate well in more minimalist decors. Roller shades and matchstick blinds also work well for a clean feel.
Control pattern and layer texture
You can use pattern effectively in minimal spaces, but control the scale and loudness of it. Small scale and tone on tone work best. Ramp up your use of texture to create visual interest, think quilted, knobby, woven, rough, smooth etc.
Open up the space
Spaces are restful when your eye can find a place to rest . The more open spaces the more restful. Think about unrestricted sight lines in a space. Don't block walkways or windows with furniture , leave enough space to provide ease of movement. Of course light coloured furniture helps your eye move over it. Your room doesn't have to be stark. Warm it up with light textured rugs or throws.
Choose furniture with clean lines
Forget about ornamentation and frills. Don't go for overstuffed and large scale, but do go for comfort. No decor should be uncomfortable to live in.
Repetition is a wonderful soother. Consider repeating the same shape or colour to move the eye along.
Here your eye is drawn along the tea lights and flowers to the sparsely displayed art work. The repetition in the light fixture over the peninsula and in the mill work all helps the eye to wander calmly.
Nature and repetition together creates a stunning shower.
Select uniform wood finishes
The use of similar wood tones pull this room together visually. You eye moves easily from piece to piece and the lighter colour palette is soothing and doesn't take away from the wood.
Use natural elements
Include circular shapes