-Interference is a big issue as well (metal in the walls – signal will bounce right off it)
-You can get a wireless repeater(s) to increase signal strength
-buy hardware that uses WDS [WDS may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time]
-Need to find a repeater compatible with your router [same brand name, uses same wifi standards]
-For maximum network compatibility, use all of the same brand-name products
-If it’s a wireless router, turn on WPA encryption [improved data encryption and user authentication]
-Hide your broadcast ID or MAC address filtering [identifies your specific computer, network card, or network’s internet address]
-Turn off Universal Plug and Play (UPnP) [allows software to change router settings without user interaction]
-Change the default name of the router [in router settings]
-change default router password [something not easily guessed or in the dictionary]
-Turn off WAN administration [refer to user manual]
-access your wired or wirless router by typing 192.168.0.1 or 192.168.1.1 in your internet browser
more info: http://www.wirelessnetworkproducts.com/index.asp?PageAction=Custom&ID=21
partial source: techguylabs.com
Posted by techqa 
Tech Help 