There are many relaxation techniques that work.
Some people enjoy meditative techniques.
Others find listening to their favorite music, reading a book, or soaking in a warm tub relaxing. Whatever works for you is fine. Here's a simple breathing-based technique that's easy to learn in principle. How much benefit you derive from it depends on how often you practice it. When I first started using this technique almost 30 years ago, my initial sessions didn't produce the kind of deeper relaxed states that I was able to accomplish months later.