Your wifi antenna is most likely omni-directional, meaning it emits a signal equally in all directions. The best position for the router is in the center of the home / office and as high as you can place it. If you need to place the router near the edge of the home or office, then consider creating a directional antenna device. All it takes is an empty tin can.
Empty the contents from a soda can or beer can. Using a knife, carefully cut the bottom of the can off. Next cut the top of the can nearly off, but leaving it uncut near the drinking spout. Then cut the body of the can in half. Spread the can apart and place it over the existing antenna and directing the signal to the desired areas. The area behind the tin can will have a much weaker signal because the direction of the signal is being forced towards your desired area of the home or office. Done.