1 install WiFi Analyzer on your phone or tablet and see what WiFi signals you have in your area, what channels they are on.
2 Go into the settings of your router and change the broadcast channel from auto to one of the channels with little to no other signals on it .
If you have 2 different routers in close proximity both on say channel 2 they will cause constant signal drops and interference. Most 2.4G routers default to channel 1/2 and 10/11 . Hence mine are on channels 4 and 8 So they do not interfere with each other or the neighbors.