Every company with any degree of success or experience already has a number of good practices in place currently. Without any guidance as to what makes good practice, companies would be reinventing the wheel every day, and ultimately they wouldn't be able to stay in business.
ISO is a management system that gives good business practices on how to ensure three core aspects of quality assurance:
ISO can be used by any organization, large or small, whatever the field of its activity is. Evidence of this is the fact that over one million companies and organizations in over 170 countries are currently certified in ISO 9001, and this number is on the increase because of its promised benefits to your business.
If you want to get an idea of how close to certification you already are, learn more about ISO implementation here.