Here are a few things you can check:
Do you have a restricted profile on your device? Always make sure that you’re logged on as owner and not user when downloading apps for restricted profiles.
Do you receive an error message? Find out what the error message is and email us. Or if like to research yourself and learn a thing or two — google it. The Google forums are usually pretty up to date with error codes.
Do you have enough free space on your device memory? Check the available space on your device. If it’s less than 3GB you may want to transfer some apps to your SD card. Remember that a lot of apps can’t be installed on your SD card, so you always want to make sure you have enough space on your internal memory.
At last but not least, try deleting the app, rebooting your device and download it again. Sometimes a good old reboot will do the magic.