After working with this method for a period of time, you will gradually see the image come into focus. Be patient and do not get down on yourself if you have trouble seeing. For some, this comes quickly and easily, while with others, it takes longer. When a mantra has no visualization, simply sound it and know that the power of your own soul, along with the mantra, working together, will achieve the correct results which will most benefit you. Trust that and allow it to be.
Repetition is important.
The more a mantra is used, the more powerful it becomes, thereby achieving the desired results. When sounding a mantra, it does not need to be done loudly. However, the voice should be deep, bringing the sound all the way up from the diaphragm. Simply sit quietly and relax with the eyes closed. Take a few deep breaths, see the visual-ization in front of you and sound the mantra.