Test the important rooms
Compare the same device and task near the router and where coverage is poor. Keep a note of results. A slow internet line and weak room coverage can need different remedies.
Choose an open, practical location
Check ventilation, cable reach and nearby obstacles before moving the router. Walls and metal can affect signal, but no placement rule guarantees the best result in every building.
Change one thing at a time
Try a candidate position, repeat the tests and keep the better evidence. Do not disconnect equipment that also provides telephony or another essential service without a plan.
If placement is insufficient
Consider a compatible access point, mesh or cable route based on the remaining weak areas. The radio path between equipment matters as well as coverage to the phone. An extra unit is not automatically a cure.
Questions about this guide
What should I change first when trying a new router position?
Try an open position nearer the areas you use, within the connection and power constraints. Compare the same device and task before and after the move.
Should I put the router inside a cupboard to keep it tidy?
Check signal and ventilation before doing so. Cabinets and nearby materials can affect coverage, and the manufacturer's ventilation requirements still apply.