Settings> Mode location> High precision / saving battery / single device. You'll have to choose one of these 3 options to enjoy a good GPS signal because if you detect the location, you can play Pokémon GO normally and capture Pokémon.
In my case, of the above options, I have marked the high accuracy, because often scoring more with the sites. But Pokémon GO spends a lot of battery, and it is important that you combine it with the option of saving battery, you certainly enough. So, Pokémon GO find your location without problems.