Option-Click on the WiFi icon -> Wireless Diagnostics

Click on Wireless Diagnostics -> Window -> Scan

Expand the scan window so you can see the things to the far right.
The one item in bold will be the WiFi base station you are using.
You want to make sure the channel your base station is using is the strongest one your Mac sees in the location you are going to be using it.
RSSI values in the -30's (excellent), -40's (Great), -50's (Good) are preferred. Values from -60's to -90's are moving towards the weak side.
Noise values in the -90's (no noise), -80's (a tiny bit of noise), -70's (noise is getting stornger), -60's (noise may start to be a problem), from here going down towards the -30's is way too much noise on your channel.
Now look at the other WiFi base stations listed. In the 2.4GHz frequences, you want to be on 1, 6, or 11 if possible. You do not want anyone to be on any channels 2 below and 2 above your 2.4GHz channel as each channel actually takes up a total of 5 channels worth of bandwidth.
If you have overlapping channels from other WiFi base stations, you need to evaluate if their RSSI is strong or weak. If they exist, but have an RSSI in the -80's -90's, and you have a nice strong RSSI, then this is not a problem. What you do not want is overlapping channels that are very strong.
The 5GHz channels do not overlap, but you again want to look at the RSSI and Noise values, and if there is conflicting WiFi base stations, if they are strong signals or very weak.