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You want to choose the channel that has the least possible interference from neighboring networks. You will need to determine what channels are used/not used nearby. If you live in an urban neighborhood or apartment, it may be impossible to find one that is completely unused, but you can identify the strongest signals, and choose your own channel to avoid overlap as much as possible. The easiest way is to get an app for your Android or iPhone. I use WiFi Analyzer, but there are other options that are probably just as good. There are also applications available for PCs and Macs, but the nice thing about the smartphone/tablet apps is that you can easily move around to asses the signal in different locations around your home/office.