What wireless channels to use ?
The 802.11 b/g WiFi standard defines a total of 14 frequency channels. The FCC allows channels 1 through 11 in the U.S., and most of Europe allows channels 1 through 13.
WiFi channels actually represent the center frequency that the transceiver uses (e.g., 2.412 GHz for channel 1, 2.417 GHz for channel 2, etc.). There is only 5 MHz separation between the center frequencies, and the signal occupies about 22 MHz of the frequency spectrum. As a result, an 802.11b/g signal overlaps with several adjacent channel frequencies (by 11MHz on each side of the center frequency). This leaves only three non-overlapping channels: 1, 6, and 11 in the U.S. to use without causing some interference between access points.
The best approach when choosing a channel is to do a site survey from your wireless client computer, or the router/access point (if available). Note the channels of nearby wireless networks. The default on many routers is channel 6.
Once you have a site survey available, just keep in mind to use non-overlapping channels (1, 6, 11), or minimize overlap of signals by using channels as far apart as possible from other networks in range.