One network, not several
Many homes end up with overlapping WiFi networks from old routers and extenders that were never removed. Simplifying to one well-placed network is often the biggest single improvement.
Wired where it counts
Smart TVs, game consoles and desktop PCs run noticeably better on a cable than WiFi when one is available. A short cable run can solve a problem no amount of WiFi tuning will.
Set it up once, properly
A network set up correctly the first time, named clearly, secured, and positioned well, needs far less fiddling later than one patched together over the years.