Light makes or breaks a photo, and when you're shooting natural light, being able to find the right kind is crucial to getting the shots you want. This great video talks about what to look for and how to shape natural light for a great portrait.
Coming to you from Sean Tucker, this helpful video follows him as he looks for a good composition and location for a natural light portrait and explains his thought process in selecting it. In it, notice how he thinks of the natural light a lot like he would a studio setup, looking for a large, soft source, using the buildings as flags to boost contrast, and improvising a reflector to bring up the shadows beneath the model's eyes and add a second catchlight. The alley and the buildings also function as a compositional tool, naturally framing the model and leading the eye toward her. After that, it's just a bit of post-processing to enhance what's already there, but by carefully thinking through the desired image and selecting an appropriate setting with the right light, Tucker starts with a strong base image that only needs light editing.
Be sure to check out Tucker's new book here.