Bold choices but it looks like a waiting room with all of the pieces lining the walls. Your drum chandy over the dining table is too small scale. Needs to be 1/2 the width of your table and hang 36" or less above it. The one you have now would look good hanging with the portrait of the girl above the buffet or in a powder room or foyer. Lower all your art. Free standing art with centers at 60" above the floor. Pieces with furniture 4-6" above the piece they're with. Don't hang a mirror in the dining room unless it will reflect something beautiful or interesting like the view from one of your windows. Turn your rug the other direction and put the sofa on it perpendicular to the division between the two windows. It should face the single window. Flank the sofa with the two striped chairs, facing each other over the table you have in the corner. Try the striped bench/hassock in the corner where the table was. Raise the curtain rods to the ceiling. If the curtains are too short to kiss the floor, add a wide bold panel to the bottoms in the bright orange of your pillows. I think you should add a fun element like a bright orange bean bag chair on the floor in front of the window. If that is too much for you, add orange or yellow lumbar pillows to the dining chairs.

I would paint your bookshelf the same colour as the walls and stuff it with, well, books! I would paint the built-in corner unit to match and just use it for potplants - ivy that hangs down would look good. As for the coffee table, if the room is small, what I did in our little family room was hunted around and found a large curved hunk of tempered glass from Freedom and it sort of 'floats' and looks invisible in some lights. Seriously, I think the line was called Ghost and was very reasonable (they also had a side table to match). Throw a bit of cherry red around and see how it looks with the creams and the taupes. Here is a pic of the coffee table.

I think the first task is to repaint the walls. In your pics the wall colours appear muddy, while the painting colours are bright and clear. The two are fighting each other. Neutral paint with a blue-grey undertone would work with the painting, the rug and the lounge setting. Don't make it a feature; let the artwork be the hero--as long as you love the artwork! The room as a whole is quite hard and needs some texture. Timber accessories would be a way of softening it. Maybe consider adding a couple of timber stools in one of the paler tones (oak?) to use as side tables. One way to soften the corner to the left of the TV unit would be to add some floppy baskets in a natural material like seagrass, again in a pale colour that would tone in with the timber. You could use the baskets for storage of magazines and books, which would also add texture. Greenery in the left-hand corner would also add texture. Maybe one large plant could be placed behind either one large basket or a couple of smaller baskets or softly textured containers. Otherwise, a row of three small plants somewhere on the TV unit would be cute. I agree with you about using blue tones from the painting as accents, but only if you tone down the blue. It has to be the same colour but much less powerful and overwhelming. You could also use some of the beautiful sea-green shades, but again with a softer tone rather than the strong colour used in the painting. Cushions in a combination of blues and greens--but much softer than those in the painting; they are way too strong-- would look great against the dark grey lounge setting. I would ignore the purple, black and grey when choosing accessories. Floor cushion(s) in blue or green, or patterned subtly in these colours, are another simple idea to add both colour and texture. Coloured glass or textured timber bowls, plate or vases on the TV unit would work and are often quite cheap to buy. Books always make a room look homely. Even a stack on a stool add interest and texture. Apart from the painting, most of these items can be bought quite inexpensively if you look around. Good luck!!

You’re right it is to light up a dark corner. Look elsewhere in house