Without knowing what state you live in it might be hard to answer. In Michigan there is a League of Michigan Bicyclists and it's a good resource for information on bicycle advocacy and bicycling in general.

I would start by checking with your local municipal governing body, move to the next level at the county then the state. Your LBS should have some information and any bicycling clubs and groups in your area should be a good resource. It's a start. You can certainly go it alone however many voices together make a louder voice. Even having said that, one person can effect change.

You may also look to any transportation agencies in your community. Where I live the county has adopted "complete streets" and there are goups and agencies that promote non-motorized transportation as part of overall transit planning. Again, it's a start.