The paper presents procedures for a cognitive assistant's behavior planning based on scripts - generalized schemes of tasks solving. A cognitive assistant is a virtual intelligent agent that has its own worldview and builds a worldview of the user, it helps to solve various common or specific problems. The key component of assistant's goal-based behavior is scenario - a reusable abstract sequence of actions and situations that are used for synthesis of a concrete plan of actions for a user. The concept of a scenario in psychological and linguistic interpretation as well as the procedure of scenarios extraction from texts are considered. The scenario and the plan of behavior are formalized using the sign-based approach. Methods for synthesizing a plan of behavior are proposed. A test case of a behavior plan synthesis for buying a car is considered. © 2022 Federal Research Center "Computer Science and Control" of Russian Academy of Sciences. All rights reserved.