The best way to reserve an ad is to:
- A) Create a reservation campaign in AdWords
- B) Contact a Google sales representative
- C) Create a standard video campaign
- D) Enter specifications on the “Reservation” tab
You can contact Google representative concerning custom thumbnails for video ads or ad reservations for example.
As an advertiser or ad agency, you can buy placements on a reservation basis-instead of through the AdWords auction–when you want to pay based on the number of impressions (also known as cost-per-thousand impressions) or per day (cost-per-day). Reservation campaigns also let you buy impressions at a fixed rate.
Read more here: https://support.google.com/partners/answer/6030919