Set up to track mobile application downloads for Android

racking app downloads from Google Play doesn't require adding a code snippet. It can be done with no changes to your app's code. Simply follow the steps below

Sign in to your AdWords account at http://adwords.google.com

1. Click the "Tools and Analysis" tab, and then click the "Conversions" tab.

2. Click the "+ Conversion" button.

3. Name your conversion, select "App download" and click "Save and continue". Enter the package name. (You can find your package name by looking up your app in Google Play. It's the part of the base URL that identifies your application:"https://play.google.com/store/apps/details?id=<package_name>")

4. Click "Save and continue".

5. On the next screen, click "Done".

6. Your app downloads conversion data will now start showing up with the rest of your conversion data within 24 hours.

Note: Application download tracking for Android will only work if your links in Click-to-download  or Mobile App Extension ads point directly to the Google Play Store. Third-party tracking URLs are not supported at this time.

                                                    Click-to-download
If you want to make it easier for people to download your mobile app, you can begin by creating a click-to-download ad. This kind of ad allows people to download your app from iTunes or Android market after clicking on your ad.

When you create an ad, you can choose to create a click-to-download ad. When you enter the display URL for the ad, include the URL "itunes.apple.com/" or "play.google.com/store". When the ad is running, the display URL will show that an app can be downloaded from iTunes or Google Play.
If you include a full link to where the app can be downloaded in the "Destination URL" field, Google will automatically find and display the icon that's registered in the iTunes App Store or Google Play.
Example   Android
Display URL: play.google.com/store/
Destination URLs:
Search results page: http://play.google.com/search?q=pname:com.example.appname
App details page: http://play.google.com/store/apps/details?id=com.example.appname
To build the destination URL for Android apps, you'll need the app's "fully qualified Java package name." Once you have the package name, insert it into one of the following URL structures:
1. http://play.google..com/store/search?q=pname:
2. http://play.google.com/store/apps/details?id=pname

For more Detail follow the Following link
http://support.google.com/adwords/answer/1722054/?hl=en
http://support.google.com/adwords/answer/2549053
http://support.google.com/adwords/answer/1722117
http://support.google.com/adwords/answer/1722057