Request google to remove it but that can take time so if possible return a status code of 410 on all pages you want to be removed for a few days, Google react quite quickly to this status code as it means the page has gone and not coming back.
Once the page has been removed make sure you have added rel="noindex" to the head of the page, this will prevent google indexing it again. There are many examples of how to do that depending on your platform, simply search noindex on google.
The final bit, sure you remove the noindex once you are ready for the page to go live.