Google is offering a FREE $10 Google Store Credit when you sign up for the Google Store newsletter. Your free $10 code will be sent via email with the subject "Welcome to the Google Store" (check spam folder). This offer is for first time subscribers only and valid on Google Store purchases, not Play Store, until 12/19. Click here then scroll down until a pop-up appears that says "Get $10 off your next purchase" (view image screenshot below). Sign in and sign up or enter your email address" then just sign up for the newsletter and get your free $10.
This offer may not appear for everyone and will only be available while supplies last. It could end at anytime so let us know if it still works for you.