With basically a blank canvas you could add any colour as long as it was light and bright. Add some cushions, a rug and throw that tie together. If you have some art to put on the wall use a colour from that to begin with. Re the curtains .... Keep it simple. See what your other additions do first. Good luck.

First thing I'd do is throw the grey carpet up onto the sofa. Meaning it's colour.
Introduce a thick grey throw, loosely folded over one of the seats, up over the back then layer your cushions in front of that. Building up onto it will scatter your colour palette around and start bringing it all together. It will be softened. However keep your colours to a minimum, perhaps 2. This does not include tones of colour, as many as you like will add interest and sophistication. In a chocolate and grey interior, it could be luxe, but I am thinking shades of salmon and mustard up against creams and greys.
You also need to link your walls to the sofas, as the floor area looks heavy in comparison. To correct it you either introduce the wall colour down onto the floor, or the floor colour up onto the wall, it will balance it out. I'd place large black frames with rich colours of chocolate with perhaps gold leaf or metallics. Keep it abstract to be modern, or even go the opposite with some classic charcoal pencil sketches in a pair of large frames. The images will start to personify your space, so choose the context of the image that you can continue a theme from, like architecture where you can place related objects on a side table, even coffee table, I love tables with reference books that on a Whim you can pick up for inspiration. It shows who you are and what you aspire to.
Or it may be floral, landscapes, paintings whatever, find something that works.
Don't necessarily go looking for art, you can make it, save an image online, print and frame to suit you and your budget. Even an a3 image can be framed in a larger frame to make a bold statement, just add a frame Matt that you get from a picture frame shop.
Ikea also have ready made large frames too.
For some reason emerald green keeps popping into my mind when I look at your room, maybe some plants, foliage can liven a space but also, slight little traces of it around can freshen a space. Maybe thin picture frames, or spines of books can bring this in.

Open your curtains and take a photo during the day with as much light in, as the couch and carpet look brown in these pics. Hard to give ideas if your saying grey? cheers

You have two neutral colours (grey and brown) which need an addition of another colour and some pattern. See rug and cushions lamps and art