With your original pictures - I agree with larger rug. But I don't agree with comments suggesting the rooms are monochromatic. They are lively indeed. I think you are just missing some accessories! Art work on the empty walls - even just a single large dramatic piece is in order. In the bedroom on the white wall, in the living space behind the sofa, in the greenish bedroom behind the two beds. Those are instant areas where you can improve. But I think your spaces are lovely and well put together. Also I agree with the comment about table lamps - some of those would really add something, and your coffee table looks so empty - maybe just one gorgeous bowl, or stack some books. These rooms are 90% done in my opinions, just need a few finishing touches. Some of my rooms come out like this because the clients are not willing to pay for those last few finish items or feel they can do that part themselves...

I like the ceiling. I think the hanging lights are too fancy and distract from the ceiling decor. A simpler light would look better or sticking with the canned lights you have. The walls have too many big, black things on them. It's hard to tell if they are windows with shade --- in which case I'd pick something lighter, perhaps to echo the ceiling, TVs (how many do you need?) or what. I'd consider a big piece of statement art in the place of at least one. If you're on a budget, get a large, high quality photo in the right colors, you can take it yourself. Sepia and black architectural might work. I like more color and more natural light. You may have closed the shades for a better picture, so it's hard to comment on the light, plus windows are a feature of your room, not exactly a decorator's choice. I would consider how to get a few small pops of color in, pillows, flowers, candles, maybe even a runner rug along the right wall. If you are doing this as part of a portfolio, the entire ensemble would look more welcoming with a few touches like someone lives there. Something on the coffee table, for example. A few books and a candle. A tray with tea things, a vase of flowers or basket of fruit. Pick one or two things and make it composed. You see this a lot in designer Houzz photos. Here's an example, you note this picture would be a lot more stark with an empty table: https://www.houzz.com/photos/21-house-contemporary-living-room-san-francisco-phvw-vp~60642

I am an amateur lover of home decorating. I too have a very awkward long narrow living room that is 350cm by 620cm. Additionally it has diagonal traffic flow from the front entry to the rest of the flat. The owners have built a cabinet at one end for the TV, etc. I think I would make a cosy seating area at one end of your long living room. Place a grey or brown sofa at one end but not against the wall. I like the idea of a narrow console table behind the sofa with a table lamp, a plant or a large statue. This brings the end wall closer in. A peachy or raspberry carpet in front of the sofa will pick up the wall colour and anchor this seating area. (grey and some browns also coordinate with raspberry/peach). A couple of raspberry sofa cushions can help include the wall colour into your overall scheme. Single chairs opposite the sofa allows visual and actual flow down the narrow room and completes this seating area. At the other end of the long narrow living room I would place a reading chair, a floor lamp and a small round coffee table. If there is room you could have a tall bookshelf with you favourite books. What do you have on the long side walls? I have windows and doorways on both long sides. I decided to use pull up shades on the windows instead of curtains which I thought would make my narrow living room look more narrow. The wall colour is white but I think I will tone it down to a soft grey. I plan to paint the end walls a darker grey.

Depends on what effect overall you want -- hot tropical feel (oranges and reds) or a bit more toned down? You can take inspiration from pictures of gardens with lime green heuchera or sweet potato -- often paired with chocolatey purple, silvery greens and blues.