1. A computer-implemented method comprising: receiving, by a server system, user enrollment data of a particular user from a user device of the particular user; generating, by the server system, a user profile for the particular user based at least on the received user enrollment data; selecting, by the server system and based at least on the user profile, a first subset of customization rules from among a set of customization rules associated with an application configured to operate on user devices, wherein the first subset of customization rules are selected by the server system for the particular user and do not represent user settings specified by the particular user; providing, by the server system, user interface data specifying characteristics of a user interface of the application to the user device of the particular user, the characteristics of the user interface being determined by the server system based at least on the selected first subset of customization rules; saving, by the server system, a first set of parameters that specifies the characteristics of the user interface determined by the server system based at least on the first subset of customization rules selected by the server system for the particular user; and after providing the user interface data specifying the characteristics for the user interface to the user device of the particular user: receiving, by the server system, (i) user interaction data indicating interaction of the particular user with the user device, (ii) application use data indicating a pattern of use of the application by the particular user over time, the application use data indicating a frequency or extent of use of the application by the user after the user interface data is provided, and (iii) sensor data from the user device of the particular user; assigning, by the server system, priority scores to the user interaction data, the priority scores including a first priority score for user interaction data obtained at a first time and a second priority score for user interaction data obtained at a second time that is different than the first time; without user input specifying a change in preferences, determining, by the server system, that the particular user would prefer a change in the user interface based on a difference between the first and second priority scores exceeding a threshold amount; selecting, by the server system, a second subset of customization rules for the particular user based at least on the user interaction data, the sensor data, and the application use data indicating the frequency or extent of use of the application by the user after the user interface is provided, wherein the selected second subset of customization rules includes one or more customization rules that are different from the first subset of customization rules, and wherein the selected second subset of customization rules do not represent user settings specified by the particular user; and providing, by the server system and to the user device, updated user interface data that adjusts the user interface for the application based on (i) the saved first set of parameters that specifies the characteristics of the user interface determined by the server system based at least on the first subset of customization rules and (ii) the selected second subset of customization rules, wherein adjusting the user interface comprises: in response to determining that that the particular user would prefer a change in the user interface, determining, by the server system and based on the second subset of customization rules, that a characteristic of the user interface having a current state should be changed; and providing, by the server system and to the user device, updated user interface data that gradually changes the characteristic from the current state to a second state over a series of multiple sessions of the application, wherein changing the characteristic comprises providing a different updated user interface for display in each of the multiple sessions, the updated user interface of each session having been adjusted so that the characteristic is incrementally closer to the second state than the updated user interface of the preceding session, wherein the updated user interface of each session of the multiple sessions is a combination of characteristics of the user interface of the preceding session, as specified by saved parameters describing the user interface of the preceding session, with characteristics determined using a respective subset of customization rules that is selected by the server system, from the set of customization rules associated with the application, based on user interaction data and sensor data generated during or subsequent to the preceding session.