1. A method comprising, by a computing device: receiving, from a client system of a user, an indication of the user accessing a query field of a currently accessed interface of an online social network at the client device of the user, wherein the query field is in a null state; generating a plurality of structured queries that each comprise one or more unique query tokens referencing one or more unique objects associated with the online social network; calculating a score for each structured query based on one or more user-engagement factors, the score for each structured query representing a probability that the user will engage with the structured query; and sending, to the client system responsive to the indication of the user accessing the query field, instructions for displaying one or more suggested queries on the interface, wherein the one or more suggested queries correspond to one or more structured queries, respectively, having respective scores greater than a threshold score, and wherein each suggested query that is displayed is selectable by the user to retrieve search results corresponding to the selected query.