You have a good start. I think it looks nice.
My suggestions:

New, appropriately-sized art for above the fireplace. Something that contains a bit of color and demonstrates warmth.

The coffee table feels a little cold. Either change it out or put a beautiful round bowl or tray on it with decorative accessory or two. You can use it to hold remote control(s) if you have any.

Get a throw in maybe a camel color and lay it on the red leather chair. Something like LINK: http://www.brundeviantiran.com/r5_trans/produit/en/plaid-baby-camel-gp.jpg

The rug is nice and neutral, but it doesn't appear cozy. Consider changing that out if you really want to hit a home run.

Drapery panels or roman shades might further soften the space, but I would need to see the windows to make detailed recommendations.

Question: what are the cushion thingies on the top of the back of the couch?

I like your wall colors.

More bright color in pops and accent, e.g. hot pink, lime green. Something lovely and eye catching like an incredible little lacquered cabinet or beautiful piece of table art. All your furniture is very nice (extremely nice and well-chosen, in fact) but it's more background-type stuff - well-behaved supporting players waiting for the big name stars to arrive so the show can begin. Go find those stars.

Stars are outrageous and over the top....almost TOO much. But without them, the show (or the living room) is just....yawn.

https://www.houzz.com/magazine/10-inspired-ways-to-refresh-your-mantel-now-stsetivw-vs~5948948

How about a little bit of a soft yellow in accent pieces and a touch of nature. Plants,rocks,wood,shells

lovely color in your space! an ottoman would be a nice look, a throw and something with the clock as a collage of pictures/wordart/more clocks or replace with something bigger. A bigger floor plant in the corner would be stunning against all the light from your beautiful windows

It seems that most of the time we tell people to remove clutter but in your case it seems as if your room is begging for more! The red chair is great and a good start for accessorizing. Spread other pops of red throughout the room. I agree with others ... A throw, pillows and art. I might suggest just using one of the antique chairs and a small table to the right of the fireplace to open up the area a bit.. As arranged now, it looks too closed in..... Great Bones and a good start!

Mix some camel in there, interesting art piece overmantle.The two side chairs are great, although the tables may be a little big. (Too big is better than too small, it must be said.) Some stuff on the coffee table - stacked books, large bowl as mentioned above, etc.

Fabric would also help - print, velvet. etc. in pillows or a piece of upholstery somewhere.

But you have a beautiful room there. Doesn't need much at all.

I think you have too much "hard", leather, coffee table etc. and not enough "soft". Add drapes and oomph up the mantel.

Before you get in to spending tons, try to bring in warmer accents. Put up some shades on the windows or at minimum some valances. The one thing I would probably suggest you re-purpose is the coffee table. It is too overpowering. And then add strong accents to the mantle, a sofa throw and family photos here and there.

It's a lovely room - great trim, fireplace and transom over the door, and great natural light. I think the problem is that everything is very square. Fabric and shape do a lot to warm it up:

1 - I would replace the two square tables with an oval cocktail table and a round table between the two chairs, with glass tops in a antiqued or burnished gold (not shiny brass). Silver or black are too cold. (You need a minimum of 12" foot room to maneuver, and more room in front of the fireplace.)
2 - Definitely invest in some custom-made draperies for the long windows next to the door, trying to match the wall color for the background but with touches of black/red/green throughout (They are not that expensive to have made, I've done it in two rooms). Make sure they touch the floor. Also have a scalloped or D-shaped valance made for that small window to match.
3 - A mirror with a frame that nods to the metal on the new tables, or a leaned grouping of metallic photo frames in 8x10 or 11x14, would both look great on the mantle. If you hang a mirror or picture over the mantle, then a grouping of tall candle sticks, a faux birdcage, a small mantle clock and some greenery elements grouped in threes at either end will also look great.
4 - Next to the red chair I would take away the small table and put a floor lamp - black with a cream shade - there doesn't seem to be any indirect lighting. Actually I would angle the red chair into the corner, get an ottoman or foot stool for it, and put the lamp to the left of it.
5 - A lumbar or small square pillow in a color that matches the entry wall for the red chair, a throw of the same color for the couch, and two pillows in each corner of the couch (maybe a stripe and a solid each). Cotton, linen, or twill are easy care.
This is my first time commenting - I hope it's not too opinionated/overwhelming!

Also, think about changing out the planter with one that has softer lines and more color.