Spontaneous Complement can make you a conversation champion. Especially If you want to have a conversation thread with a stranger, this will definitely help you . You often come across situation when you see someone with cool clothing or a cool style in general. Here you can add the magic of spontaneous complement and you can say
Wow you've got great style!
Are you a fashion designer?
if you see a well trained dog you can say
That's a great dog!
Are you a dog trainer?
You might hear an answer like this
Oh not really!
it's just my hobby
If this spontaneous comment is delivered well, the complement will make the person feel good. So it gives you a great chance to get a conversation thread. So you can continue the conversation without feeling awkward.
But one thing you should keep in your mind that you should not compliment about their bodies because it will make them uncomfortable.