For as long as I remember I've used my Mac to hold my master address book (ok since late 2002 when I switched to OS X). Over the years it's been synced ad-hoc to Google Contacts (remember Address Book used to offer an easy sync when Apple and Google were in bed together) but the google side has always been a bit messy.
Part 3: Contacts
Since I want to maintain iCloud as my master address book for now, it's handy that Apple implement their service as CardDAV.
Fortunately Android Play Store has a plethora of CardDAV sync apps, and I chose to use one called CardDAV-sync and it seems to work fine so far (after giving it a few minutes to pull down all the details from iCloud).
The app offers two-way sync by default which should mean any new contacts entered on my phone find their way into my address book.
When configuring the app all you need to know is your personal iCloud credentials and Apple's contact server - sensibly enough named 'contacts.icloud.com'
Type all that into CardDAV account setup and you should be good.