While remembering Radha Krishn and meditating on Their Divine form, you have to chant Their name, virtues and leelas with tears of love and longing, and with a deep desire to receive Their Divine vision and Divine love. During devotion, loving meditation on Their form is most important. You may form Their image in your own mind according to your liking. You may take the help of a Deity or a picture of Radha Krishn. But, whatever form you create in your mind, you must have Divine feelings in that, because the body of Radha Krishn is always Divine and Blissful.