Most dogs are not inherently aggressive, and will not actually attack you without some pressing reason. Don't give them one.
If you see a loose dog in a front yard, cross the street. Give his territory a wide berth so that he won't feel the need to protect it. If he's just wandering willy-nilly down the street, stop where you are, scan for escapes, shields, and weapons, and wait for him to go his merry way. Continuing to walk toward him could be seen as a challenge, turning around and walking the other way leaves you blind and vulnerable, and might trigger the dog's chase instinct.
Do not approach people with unfamiliar dogs, even those on leashes. Exclaiming, "Hey, Bob, long time no see!" and thrusting your hand out for a shake can look very much like assault to a dog. Even a relatively social dog can become overwhelmed by protective instinct and have his choppers sunk into your hand before either of you realize it.
This is particularly true of children who are accompanied by dogs. You may want to pinch the cheeks of cherubic little Andy, whom you haven't seen since his Christening three years ago. Resist the urge. Whereas a dog's master is his food source, the children in the family are the pups of his pack. He will defend them if he feels they are being threatened.
Parting Words
There is no need to immediately go on the offensive and put up your Don Knotts karate hands with every strange dog you encounter. I only suggest that you be prudent, be aware, and assume nothing.
I'll leave you with what I tell my customers when I ask them to put "Genghis" away, and they insist that he'd only "lick me to death":