1. A method of managing assets of content items to be displayed on client computing devices, comprising: transmitting, by a server, to a client computing device, a content item comprising a plurality of assets and instructions for controlling at least one of i) a loading priority of the plurality of assets, ii) a placement of each of the plurality of assets in the content item, or iii) a selection of a subset of the plurality assets for display with the content item; receiving, by the server, from the client computing device, an indication of an interaction by the client computing device with the content item; and modifying, by the server, the instructions to change at least one of i) the loading priority of the plurality of assets, ii) the placement of each of the plurality of assets in the content item, or iii) the selection of the subset of the plurality of assets for display with the content item, based on the indication of the interaction by the client computing device with the content item.