Don't settle prematurely on a location for the router.
Try placing the device in several different promising locations. While trial-and-error may not be the most scientific way to find a good spot for your equipment, it is often the only practical way to assure the best possible WiFi performance. Your router should be as central as possible to all your devices to help avoid performance issue.
Avoid physical obstructions.
Any barriers along the line of sight between client and base station degrade a WiFi radio signal. Plaster or brick walls tend to have the most negative impact, but any obstruction including cabinets and furniture weaken the signal to some degree. Obstructions tend to be located closer to floor level, so installing the router high on a wall may improve the signal.
Avoid reflective surfaces.
Some WiFi signals bounce off windows, mirrors, metal file cabinets and stainless steel counter-tops, lessening both network range and performance.
Install the router away from electrical equipment that also generates interference.
Avoid electric fans, other motors, and fluorescent lighting.
Adjust the router's antennas
Do this to improve performance if the best location you find is only marginally acceptable. Antennas on wireless access points and routers can usually be rotated or otherwise re-positioned to fine-tune a WiFi signal. Follow the specific manufacturer's recommendations for best results.