Summarize this article:

Stray dogs tend to be very fearful. Any sudden movements you make, or even just moving toward him normally, could look threatening to him. In turn, his 'fight or flight' response will be activated, causing him to turn and run away from you. Staying still will allow him to see that you are not a threat to him.  If he approaches you when you are standing still, allow him to smell you.    Do not  hold your hand out for him to sniff it. He may bite your hand out of fear.  Resist the temptation to pat your leg to get the stray dog to come to you. He may interpret that as a threatening movement.  Even if the dog is displaying aggressive behavior, remember that he is likely more afraid of you than you are of him. Depending on how long the dog has been a stray, he may been called repeatedly by people—even his owner—trying to catch him. Over time, he may have developed a negative association to being called. Thus, if you call him to get his attention, he may run off in fear.  If you are trying to get his attention, consider using noises that are more calming, such as clearing your throat or faking a sneeze. You could also lick your lips or yawn to convey that you are not a threat to him. If the stray dog is demonstrating erratic or aggressive behavior and you become fearful, fight the temptation to run away. If you start to run, chances are good that he will chase you. In addition, if you run away from him, you will have your back to him, which will put you in even more danger. If you want to distance yourself from him, walk away slowly and do not turn your back on him. If you are uncomfortable around the stray dog, or are unsure of the safest way to catch him, call your local animal control or a professional dogcatcher. Provide as much information about the dog as you can, such as the location of the dog (e.g., landmarks, street signs) and his breed. If you can, send photos of the dog to the animal control center or professional dogcatcher.  Leave your phone number with the dispatcher, and inquire about how long it will take someone to come to you. Keep your eye on the dog until help arrives.  Make your own safety a priority—do not attempt to interact with a stray dog that is displaying erratic or aggressive behavior.

Summary:
Remain as still as possible. Avoid calling out to him. Do not run away. Call your local animal control.