Tick Box to join mailing list when entering email on first page of checkout

Currently the only options to add a mailing list opt in checkbox is either on the order confirmation page which yields poor sign up results as most customers will ignore this/are not interested after point of sale or by adding a custom field in 'additional info' section which is already long and it seems irrelevant to add at this point - should either be just before checking out or when creating account with email address.