What is the best way to troubleshoot WiFi

Over the weekend I set up an entire unifi stack at my parents home. Did some tweaking of the WiFi and seemed to have gotten speeds up to where they should be but there still seems to be some slow spots. What are the ways yall troubleshoot to figure out why it may be slow. Specifically if we actually installed too many AP’s too close together?

For context…they live in single story “ranch” style home with lots of brick and really spread out in a “u” shape.

Is the best method actually just to turn them all on one by one and see what the speeds are or is there a better way?