Methods and apparatuses that utilize machine learning techniques to dynamically adjust the placement of secondary content that is displayed across numerous user devices over time are described. The user devices may comprise electronic computing devices, such as a mobile phones and digital televisions. The secondary content may be displayed within open slots of webpages or display screens in response to being selected for display during a real-time bidding process for the open slots. In some cases, in response to a bid request for an open slot within a webpage or display screen, a computer-implemented bid generation system for determining the selection and placement of secondary content may identify the secondary content to be displayed within the open slot, determine a bid amount for the identified secondary content, and transmit a bid response that includes the bid amount and the identified secondary content.