Where you put the router can change real-world WiFi speed by a factor of ten. Here are the rules that matter most, in order of impact.
WiFi radiates roughly spherically. A router in the corner of your home sends 75% of its signal outside. Move it to the most central room you can.
Place the router on a high shelf. Floors and furniture absorb a lot of signal at 5 GHz and 6 GHz. A router on the floor under a TV stand is almost useless 10 meters away.
Don't put the router inside a media cabinet, behind books, or on top of another electronic device. Closed cabinets cost you 5-15 dB.
Microwave ovens, baby monitors, cordless phones, and Bluetooth devices all transmit on 2.4 GHz. Keep the router at least 1 meter from any of them. Aquariums attenuate WiFi badly, water absorbs the signal.
For single-story homes, vertical antennas give the best horizontal coverage. For two-story homes, alternate antennas between vertical and horizontal so devices on different floors all get a strong signal. See our deep-dive on WiFi antenna positioning (45° vs 90°) for the exact angle by number of antennas.
Brick, concrete, stone, and metal walls block WiFi. Drywall and wood let it through. If your house has a load-bearing wall in the middle, you may need a second access point on the other side of it, no placement trick will overcome a brick wall.
"Central" is a starting point, but if you spend 80% of your screen time in the home office, place the router closer to the office, not the living room.
Run a speed test from each room before and after moving the router. Use the same device, same orientation, and the same time of day for an apples to apples comparison.