Summarize this article in one sentence.
It can be small -- trying to get people to clean up after their animals, for example -- or large -- trying to eliminate the sales tax on groceries in your state. Keep in mind that the smaller the issue, the better chance you have at making a difference. Local government necessarily includes fewer people, and because you are one of those people, your voice can make a difference in a way that it can’t among the millions on a state or national level. Is it a national law? Then you might want to enlist the help of a Senator or Congressman. Is it a state law? Then your state house representative or a state senator is the person to see. Finally, if the law is a county or town ordinance seek out the local councillor, supervisor, mayor, or county executive. How old is it? Which person or group was responsible for writing it or changing it last time? It is important to know the history of the law so you have a better idea about how to change it. Knowing how it was made or changed before tells you who needs to be involved this time. If it was a vote by the city council before, chances are it will be changed by a vote by the city council again. Ask them about the feasibility of your idea.   Can they change or repeal it in the same way? If not, what will be different this time? If it was a ballot measure (this is only true for some states), ask how to get your changes on the ballot again. You’ll need to know when to file your measure and how many signatures (often 1,000+) it will take to get it back to the voters.

Summary:
Discover an issue that you are passionate about. Know what level of government is responsible for the law. Read the laws governing your issue. Talk to the people or group that made or changed the law last time.