To catch the natural ambient light like in this image, make sure you have your flash forced off. You can also use the "Candlelight Mode" if your camera has this setting. Make sure you hold real still as the camera's shutter needs to stay open longer to catch the light. If your camera or lens has a stabilizer on it, you want to make sure that it is on. This will help to compensate for any subtle movement you might make that could compromise the image sharpness. Using candlelight will make a dramatic portrait in a way that using the on camera flash just can't replicate. Because your eye often goes to the brightest part of the image and is attracted to points of contrast, the subject becomes the focal point of your photograph.