Checkmate the opponent's king.
Chess Game Strategies

one strategy is to play like Tigran Petrosian the 9th world champ, basically play ultra defensively and bore your opponent to death until he ultimately makes a mistake and capitalize on their mistake

Read this:
GM Larry Evans' method of static analysis - Chess Forums - Chess.com
Posts # 4, 7-to-10 and 12. Then play over the three sample games.
It might be a bit too advanced for you, but it will probably teach you something.
Hello. What are some strategies to improve your chess game?