Choose an open, central spot
Put the router on a shelf near the rooms you use most. Avoid enclosing it in a cupboard or placing it behind a television. Leave ventilation space and keep it away from large metal objects.
Check the rooms where you work
Run a speed test near the router, then repeat in the room with poor reception using the same device. Note where calls drop or pages slow down. Try a new router position and repeat before buying extra equipment.
When moving it is not enough
For a distant desk, consider an Ethernet cable. For several rooms, an additional access point or mesh system may help. Plan the cable route and power outlets, and check compatibility with your existing router.