Harmony is created when all your elements and principles of design are working together 'in harmony'.
Some of the elements and principles of design include emphasis (focal point), line, shape, colour, pattern, texture, balance, space, proportion, scale etc.
You don't need to use 'all' of these in one room at the same time as it depends on the style you want to create.
Creating harmony doesn't mean going shopping to recreate 'that' coveted living room as presented in your favourite design blog, magazine or showroom.
Use or update/rework the pieces you do have, that you love - and then fill the gaps with some new finds on online auctions; or at garage sales and stocktake sales.
As a starting point, consider the following:
Choose a focal point
Create contrast in textures
Offer repetition and rhythm in colour
Ensure patterns don't clash
Offer even distribution of artificial light.
You would like a Scandi understated elegant and cosy living room.
(A look you can also inject into a rental property).
Go with all-white walls - matt finish if you don't have kids or pets - your white is your blank canvas.
You found a large oval gold mirror at an auction - it has potential - sand it back and repaint it in a matt chalky white. It can now be the focal point of your room.
What's the first wall you look at on entrance; or where do your eyes land when you're spending time in the room… that wall will be its home. Hang it with your eye at the centre of it.
You have an old sofa but it's so comfortable - head to your closest fabric remnant shop and purchase a piece of fabric large enough to cover your sofa - no need to re-upholster - have a sewing friend hem the edges and give your sofa the layered look.
Purchase the same fabric in a light taupe or stone colour, plain or a thin stripe; and have that same (well-loved) sewing friend make some cushion covers. Then add further texture with some faux fur cushions (that stocktake sale); and a taupe knitted throw.
With white sheepskins on the floor, you've now covered texture; but also repeated the layered look of whites and soft taupes to offer rhythm to the room.
If you do love a gentle kiss of blush pink, include a squat glass vase or worn silver jug (heirloom or garage sale) with a bunch of loosely arranged short-stem pink roses… repeat that pink in some accessories, coffee table books, or perhaps just 2 blush pink linen floor cushions or rope knotted ottomans/footstools.
Too many patterns in a room can feel overwhelming and not a place to relax in - a simple stripe will work here - repeated in the cushion, a hand-knotted rug or kilim under a coffee table; and even in Roman blinds dressing your windows… most windows are of a standard size so retail will accommodate that.
(Ready-bought curtains will be more affordable than custom made).
No space is complete without ambient light - do not rely on overhead lighting… include some occasional lamps and candles sitting on a tray on your coffee table… this could be your dad's old suitcase that you've whitewashed; or a piece of wood sitting on two piles of old design magazines (a pile each side so there's no see-saw effect); and finally, walk that closest beach or forest for some driftwood, or forest finds - natural accessories and sculptures…
Throw in some baskets and pile high with extra throws and magazines.
Sit back, put your feet on those ottomans, crack open that wine - ensure it's white and not RED!