Talk with your Neighbors
A good first step is to figure out whether motorists are speeding. While this may not change what you want to accomplish (after all, perception can sometimes be as important as reality), this may impact the amount of assistance you can get from local traffic engineers or traffic enforcement officers.
Vehicle speeds can often seem high when you are close to the roadway, even when motorists are actually traveling under the legal speed limit. This is especially true on a quiet residential street. First, confirm what the speed limit is for the street where you see problems. This will not always be posted, as some towns and cities simply establish speed limits for arterial streets and residential streets. Your local traffic or police department may have radar guns that you can borrow and use to document speeds. They may also have a speed study program that they can use to check vehicle speeds.
Talk with your neighbors or neighborhood association (if you have one) to find out who else is concerned about speeding in your neighborhood and wants to help out. The more people you have that support your cause, the stronger your voice for change will be.