Understand the Rules
There will be rules and guidelines whether you're running on the sidewalk, on a track or in a public park. Learning the running rules where you'll be exercising is the best way to avoid embarrassing yourself and inconveniencing others. This isn't just polite behavior, either. There may be city ordinances in your area that could lead to expensive citations for doing things like running in the street or cutting across private property.
You may be asked to run on a specific path, single file or only at certain times of the day. Running may not require a license, but like driving a car, using public paths and thoroughfares is a privilege, so give running venues the respect they deserves. If you study the route ahead of time you can prevent arguments about where to go next - and avoid hefty citations for running in the wrong spots!