1. A method for actuating an injector of a fuel injection system of an internal combustion engine, comprising: determining an injector parameter which characterizes an injection process using a first calibration method based on a control parameter, and determining a first feature for calibrating the injector based on the determined injector parameter; determining a second feature for calibrating the injector using a second calibration method based on an engine parameter, and monitoring the first calibration method based on the second feature; and activating the injector in accordance with a control signal that is evaluated based on the first feature and the second feature.