Is your WiFi running slowly? Do you sometimes lose your connection? In many cases, the problem arises because another nearby wireless LAN is configured to use the same channel as yours, and the signals are overlapping.
Changing the channel is easy. Just log into your router, go to the WiFi setup screen, and pick a number. But what number to use? For that, you'll need to know which networks are already operating nearby, and what channel they're set to. Thankfully, finding out such information is easy with a free utility such as InSSIDer (so-called because the name of a wireless network is known as its SSID).
As you can see from the picture below, the utility shows the name of each network it finds, which channel it's using, which method of encryption it's configured for, and more besides. All you need to use is a Windows PC (desktop or laptop) with WiFi capability. Once the software is installed, press the Start Scanning button and then just watch the results as they are displayed.
An analyzer such as InSSIDer has other uses too. For example, if you're setting up a new WiFi network, you can ensure that your channel number doesn't conflict with any other network in the neighborhood. And because the program shows the signal strength, you can get maximum performance from your hardware by adjusting the position of the router and/or the antennae while watching the effects on the screen.
While there are many similar freeware utilities around, such as NetStumbler, I personally find InSSIDer the easiest to use and install. Check it out at http://www.metageek.net/products/inssider.