What is the best way to configure an apple airport express to get fast wifi where there are many neighbor wifi networks?

The networks around you can be in two different frequency bands, the 2.4GHz band and the 5GHz band. If all of your devices support being a client in both bands (they will say they support 802.11a/b/g/n if they do), it would be wise to invest in a "Dual Band Dual Concurrent (DBDC)" router and have the majority of your personal devices connect to the router in the 5GHz band rather than the more crowded 2.4GHz band. Many dual band client products today will actually prefer to be in the 5GHz band if you give both the 5GHz and 2.4GHz networks hosted by your DBC router the same network name. Alternatively, you can give the 5GHz network hosted by the DBDC router a different name (e.g. "MyNet-5G") from the 2.4GHz network (e.g. "MyNet-2G") so that you can explicitly make devices in your home always connect to the 5GHz network. To do this make sure you get a router labeled as ""Dual Band Dual Concurrent" or simply "Dual Band Concurrent", otherwise the router will only do 2.4GHz *or* 5GHz depending on how you configure it, not both at the same time. If any device you have is a 2.4GHz-only device, it won't see the "-5G" network your router advertises if you go the route for having a separate network name for each frequency band. I currently have my DBDC router configured with the same network name for both bands because most devices today will flip flop back & forth between both bands without you even knowing it depending on which one is currently giving the device the best throughput. This could be more important for devices you carry around the house as opposed to stationary devices which never move.