Where do you start? It's different for everyone. Some will look to create change from within - working within their office or institution. Some will take the time outside of the work day, and volunteer time on committees or within community groups. Some will doing it by participating in recreational activities with others (like group rides). Others may have influence over a smaller circle of people, like their family or close friends. Taking the time to create and nurture relationships will enable any change to happen.
Change takes time to happen. Don't expect things to happen overnight. Sometimes things will happen fast, and then sometimes things will happen. really. slowly. Just be patient, and enjoy the ride. Patience and being a good listener are good characteristics to have or practice when you're working with a group of people. If you are working on creating change in and for a bike community, get to know the people you're working with, make some friends and have some laughs along the way! Fun and work is a balance in these situations. (Don't take it too seriously.)
Celebrate the wins - however small. This is a key thing I learned when I attended a Winning Campaigns Training this past fall in Columbia. Not only did I meet some great people from around the state and region, but I also learned a lot of great things. (I recommend attending if you get the chance!) One of these things was you should celebrate all wins. Get the city council to consider your request for adding a greenway to get to the park? Celebrate! Have the local paper do a positive story on the struggle to put in a bike lane? Celebrate! Celebrate the small wins on the way to the overall goal, and it will help sustain a group's energy and interest.
Change takes time, but with a lot of effort and some luck, good things will happen.
Be the change you want to see in the world. -Ghandi