1. Open the Settings application on your device.
2. Choose Mail, Contacts, Calendars from the Settings menu.
3. Select Add Account... from the Mail, Contacts, Calendars menu.
4. Choose Other from the Add Account page.
5. Select the Add CardDAV Account option.
6. Fill out the form with the following information and tap Next to continue.
- Server: Enter “google.com"
- User Name: Enter your full Google Account or Google Apps email address.
- Password: Your Google Account or Google Apps password. (If you’ve enabled 2 Step verification, you’ll need to generate and enter an application specific password.)
- Description: Enter a description of the account (e.g. Google Contacts).
Do the above on all your Apple devices (iPhone, iPad, iPod and Mac).
All your devices should now sync and keep your Contacts updated on all and not create duplicates.