Living room chairs get treated like an afterthought, the thing you add once the sofa's in place and there's an awkward gap by the window. I think that's backward. A good chair is often the piece that actually gets used, the one spot nobody has to share, and it deserves more thought than the leftover corner it usually ends up in.
Size is where most people get it wrong, and it's almost always in the same direction: too big. Measure the actual gap you're filling, not the room as a whole, and leave at least a couple feet of walking space on whichever side people pass through. Check the arm height against your own forearm when you sit somewhere similar, and check the seat depth too, since a deep seat looks generous in a store but leaves shorter people with their feet barely touching the floor at home. If you can, sit in it for a solid two minutes, not the ten second perch most of us do out of politeness. Pay attention to what's under the upholstery while you're at it: give the frame a gentle twist, if it racks or creaks you're feeling the frame, not just the cushion, and that's a chair that'll loosen up fast.
Where it goes matters as much as the chair itself. A heavily patterned or sculptural chair next to a sofa that's already doing a lot visually, a tufted back, a loud print, chunky rolled arms, just turns the corner into noise, and nobody can tell what they're supposed to look at. If you've got ornate or curved furniture elsewhere, a very geometric chair will look like it wandered in from another delivery. For a first chair, I'd start plain: a solid frame, a simple silhouette, a neutral or textured fabric that can take a throw pillow or a blanket without a fight. You can always add a strange, wonderful second chair later once you know what the room actually wants. That's the forgiving one to live with while you figure the rest out.
Smaller rooms and rental apartments do well with something light enough to move for a yoga mat or a dinner table extension, while bigger family rooms can carry a heavier, more settled piece that isn't going anywhere. Winter rooms want fabric with some weight and texture, summer ones breathe better in a lighter weave or leather that doesn't trap heat.
Vacuum the seams and rotate loose cushions every few weeks so the wear and fading happen evenly instead of all in one spot.