See the location of the router

Most of the people do not want to emphasize on the placement of the router. But it is important. May be you have to keep your router at little bit uphill to make your slow Wi-Fi faster. Or maybe have to place it somewhere at down. Actually, this device need to be kept in open space. Otherwise the signal may become low.

May be hindered by 

The concrete and metallic materials do stop the wave of Wi-Fi. Even some other objects may weaken the speed of the wireless signal. Especially electronic devices may be obstructed. So make sure there is nothing else around it.

Check distance from router:

As far as you go away, the weaker signal you will get for your smartphone or computer. So place the router closer to the device in which you use the Internet. If the distance increases, the signal will be slow.

Microwave as obstacle:

The home appliance, cooking machine microwave oven also became an enemy of Wi-Fi network. The calculation is scientific Microwave Oven works in 2.45 GHz frequency, which is very close to the frequency of Wi-Fi. The 2.4 GHz Wi-Fi band many times do broadcast 2.412 GHz to 2.472 GHz band.

Check if any channel Interface:

In this present day, almost all the houses may have Wi-Fi. Each flat in a complex may have a router. In this case, the problem of channel overlapping is quite possible. So maybe your Wi-Fi is strong enough, but it also gets worse in the pressure around.