High key photography involves photography where there is a large amount of light tones and fewer mid-tones or shadows. The best way to obtain high key is by using in-camera techniques rather than trying to achieve your objectives through post processing methods. Therefore, you have to learn how to create an image that has a high key tone.
Key tones are normally mid-tone. By placing them high on the exposure scale, it becomes easy to make them lighter or brighter. Thus, an image with bright mid-tones will have high tones which will be lighter or much too white.