Go to Google Play Store and download Wi-Fi analyzer. This allows you to check which channels you are using and is their any congestion or interfere with your existing channels. Since 2.4Ghz is very common on mobile phones and router it is very much possible that the channels that you use is congested.
You can then set the signal channels according to the reports. Don't go beyond channel 11.
Further to this you also activate the wall peneteration mode in the router.
Also keep your router on height for better quality signal.
channels are automatically selected but im not getting the signal from just 25 steps away, i hv enab ...
Go to webUI and under settings change the channel which are less congested. My router throws signal to me above two floors of my apartment. I am residing on 10th floor and I am able to get signal on 12th and 7th floor outside of my home. Even inside the lift.