Explain the theory behind music, which will allow the learner to not only understand how music works, but also why. Explain which pairs of notes sound good together, and which do not. Explaining this may seem tangential or distracting, but by grasping the basics, the learner's progress will be more rapid.
Clarify the system of notes. It can be confusing to a learner how the notes repeat in their pattern. To make him comfortable with how the notes work on his keyboard, you can use a laundry pen to write the letters of the notes at the top of the keys. Rub these off when he gets more confident, and he will soon begin to recognize different keys.
Explain the terminology. Although you should avoid using technical terms at the beginning, explaining the musical terminology will help the student express their own ideas to you, and you will be able to communicate more effectively. Chords, scales and tonality are all important concepts the learner should know.
Stress the importance of practice. This is the most valuable lesson that anyone learning a musical instrument can glean. By stressing the value of practice, the learner will understand what it takes to succeed at either keyboard or piano. This will also prevent them from becoming frustrated.
Explain the difference between a piano and a keyboard. If you do not want to use all of the different functions of a keyboard, you do not have to. However, showing the learner how to set a beat will help them keep time. Similarly, by explaining what they can expect on a piano will allow them to practice good habits.