A good modern table set looks like it was made for the room, low lines, a bit of air underneath, nothing fighting for attention. A bad one looks like three strangers who got seated together at a wedding, different heights, different finishes, all squared off at the wrong angle to the sofa. You notice it from the doorway before you even sit down.
Sizing is where most sets go wrong, and I say that having measured a coffee table with my foot once and been off by nearly a foot. Measure the actual gap you have, sofa to table and table to the nearest chair, and leave at least fourteen inches on each side so knees and dogs can get through without a production. For a set with a coffee table plus two end tables, the end tables should sit close to arm height, not towering over it, and the coffee table top should land around two inches below the sofa cushion, lower if you mostly use it for feet rather than coffee. When it arrives, check the finish on all three pieces in the same light, not just the showroom spot, because glass tops especially can look warm in one corner and cold and blue in another, and a scratch on the underside of a glass top is easy to miss until it is catching the afternoon sun at an angle that makes it glow like a bad omen. Check that the legs sit flat on your actual floor, not the flat polished floor of wherever you bought it, a wobble that is invisible in a showroom becomes a daily irritation on an old wood floor.
Metal and glass sets wear differently than wood ones, and it is worth knowing which argument you are signing up for. Glass shows every ring and fingerprint under a bright morning window and needs a wipe more often than you would think reasonable for furniture. Wood and metal combinations age better, the metal picking up a soft patina and the wood taking light scuffs that mostly read as character by the second winter. Either way, felt pads under anything that touches the floor and a coaster habit will save you more grief than any sealant.
If you own nothing yet, start with a simple coffee table and one matching end table rather than a full three piece set, it is easier to live with and easier to add to once you know how the room actually gets used.
Either way, it gives a room that has been looking slightly apologetic about itself somewhere settled to land.