for wireless signal 1st thing to consider is the EMI's (eletro-magnetic interference)
anything that is near that modem that produces static electricity, radio frequency and magnetic energy (eg. cordless phone, speaker, anything electronic...) isolate the modem at-least 6 feet away from this said EMI's.
2nd you may check on the the wirelss settings on your modem's GUI(interface)
see the link:http://support.2wire.com/index.php?page=view&article=60
wireless channel and power settings and the only once you should change...
channel such as 1,6,7 are sometimes used by other device (wireless phone, neighbor's router)
power settings: as you place it on a higher number it gives longer distance but gets thinner space(area)
consider the red signals as you place the power higher the signal gets longer but thiner.
lastly wireless doesnt penetrate walls/ glasses it only bounce back and forth to it... so less wall or interference the better chance of going directly to the access point...
if you really havea big house try consider buying wireless booster/repeater...