The simplest and best option is to use the import tool located within the Google Contacts interface. You can find the email and contacts import tool using these steps:

1. Login to your Google Contacts account
2. On the left, click More and then Import.
3. Select the account you want to import from.
4. Click I Agree, Let’s Go!
5. Sign into your previous email account.

Note: If you have an Apple account, please read the following article.