In order of preference.
(1) wired - if you can pull wire from where your router and cable modem are located to another location in the house where you will get good wifi coverage (with another wifi router acting as an AP/switch or straight AP).
(2) powerline connector (basically plug an ethernet cable from lan port on router into wall plug unit, other paired unit is plugged in at a location ideal for wifi coverage and an ethernet cable from that runs into the lan port of a wifi router(acting as an AP/switch) or a straight AP.
(go to smallnetbuilder to read reviews and actual throughtput, dont buy less than anything of the 500 series.)
(3) same concept as in (2) but there are similar entities using coax lines. Thus if you have a coax line between two locations (not likely from what it sounds like) you can bridge that way with two paired units.--
Ain't nuthin but the blues! "Albert Collins".
Leave your troubles at the door! "Pepe Peregil" De Sevilla. Just Don't Wifi without WPA, "Yul Brenner"