With the help of Network Detector app, you can find out the best network by roaming around the windows, balcony or outdoor spot even inside a room. App beeps when network power can offer you more than 500kbps -1mbps speed. Beep tone increases as network power increases. 3dbm rise in network means double of the network power. Just by finding optimum spot, you can increase your data speed by 20-30%.
App also provides some basic utilities like force LTE only mode, speed test, quick APN settings and network details.
Disclaimer : Data speed is subject to lot of other factors as well. So app do NOT guarantee the speed. App has algorithm to provide you best spot where your device can get best power offering good speed.