By living more simply yourself, you’re automatically helping others to live more simply too.
Whether or not you actively promote the simple life, just going through your own process is inspirational and helpful to anyone else who's dealing with the same kinds of issues that you are.
Helping others is an inevitable part of this process; it's not something you have to try to do. One way or another you will automatically pass onto others what you've learned.
You'll find that there are people around you with the same desires or similar problems that gravitate to you in some way. You may find yourself sharing your experiences, or you may not ever talk about them.
Your life experience is present in everything you do. Other people feel it, they benefit from it, and they receive a life change from making contact with you or being around you. In your own way you are changing the world.