Use channels 1,6 and 11 and use Wi-Fi Scanner to see which out of those channels will give you the least amount of CCI from the surrounding area.
Even though there are 13 channels available in 2.4GHz, only 3 of them do not “overlap” or interfere with one other: 1, 6, and 11. When a station (Access Point, client device, etc.) has something to transmit, it must wait for the channel to be clear. Put simply, only one device can transmit at a time. When overlapping channels are used (2-5, 7-10, 12,13 in 2.4GHz), any stations (STAs) on those channels will transmit independently causing degradation of performance. This type of interference is called Adjacent Channel Interference (ACI).
Look below to get a better understanding of the channels used
For 2.4Ghz planning, you should only use channels 1,6 and 11. In WiFi Scanner, you can see what channels are being used in the Spectrum graph below in blue. This will help you decide which channel is the least crowded and will give you the best signal strength.