If you have an android phone or tablet i would recomend that you download an app called wifi analyzer .
As mentioned "splitting" te 2.4 and 5Ghz wifi will also help , call the wifi name of the 5Ghz network something else.
2.4 will go further but is slightly slower ( in almost all caes this will make no difference) and more prone to congestion
5Ghz is faster less prone to congestion, but the signal doesnt travel quite as far .
A few other things can help, if your router is near a fish tank, a microwave , in the window ledge, on the floor, in a cupboard etc this can have an effect the best place for it is as central as possible
