Play strictly in time! The playing of many a virtuoso resembles the walk of an intoxicated person. Do not take such as your model.
Learn betimes the fundamental principles of Harmony.
Do not be afraid of the words Theory, Thoroughbass, Counterpoint, etc.; you will understand their full meaning in due time.
Never jingle! Play always with energy and do not leave a piece unfinished.
You may play too slow or too fast; both are faults.