The elements you see in this photograph--the position of the man's head and hands, the girl exiting the restaurant, the reflection of the automobile--existed as you see them here for only a split second. The way to ready for moments like this begins with deciding to.
Good photography, especially good street and travel photography, involves not just one "decisive moment," but a series of them. They begin with your decision to carry a camera with you rather than leave it at home, in the office, or in the car.
You have to decide what and where to photograph. Will it be the beach or the forest; the upscale part of town or the ghetto?
Most of today's cameras are designed so that you don't have to decide what exposure to use. Although this is not necessarily a bad thing, it's still better to be more mindful about exposure rather than less.
The same applies to your choice of zoom or focal length. Whatever you decide to use will affect what you decide to photograph and how.
I took this image just as this gentleman was turning the corner to my right and riding past me. He was moving so fast I barely had time to raise the camera to my eye. When I did, he laughed and said "You missed!" as he pedaled past. As you can see, I did not miss.
Let's say you happen upon a possible subject. Now you have to decide whether to photograph it or not. This is a more important decision than many novice photographers realize. The combination of activity, subject, and lighting that catches your interest could disappear in a second. If this doesn't seem like a particularly challenging decision, imagine your subject is looking right at you and standing only a few feet away. Do you raise the camera to your eye and take the shot or do you avert your gaze and sulk away?
The ultimate, culminating decision is when to release the shutter. This is what most people mean when they refer to Henri Cartier-Bresson's "decisive moment"--the moment you decide that everything fits together NOW, and maybe later too; you'll just have to wait and see.
So my tip for today is this: Be mindful, purposeful, and direct about the decisions that lead up to your photographs.
Even more static compositions like this involve important decisions, such as waiting for the sun and shadows to be in just the right place, or waiting for a diner in shadow to raise a coffee cup to his lips.