If the Google Play store gives you an error, please try clearing data and settings from Google Play and Google Play Services via the Settings -> Apps menu on your device and rebooting.
If you can't download the skin data, please ensure you have sufficient space on your device and that you have a solid Wi-Fi connection.
If your install is failing right at the end of the process - i.e. after the download and install to SD card have taken place, please follow the steps in “Help! - The game won't run!”.
For all other install issues, please create a new thread on our FMT 18 bugs forum and we'll do our best to talk you through resolving any problems you might be having with installing the game.
Such issues are rare, however they're also often device specific so we may need to ask you a few questions in order to resolve them.