When beginning piano lessons, most students make a number of significant mistakes. I've listed the most common among them to help you along. This list is deliberately limited to strictly musical matters that cause confusion to beginning pianists; mistakes in teaching method or piano practice will be dealt with separately. Without further ado, here are seven common mistakes that you should avoid in your piano studies:
The keys play pitches, and these pitches correspond to notes. F-sharp and G-flat are played by the same key on a piano, but they are not the same note. It is absolute vital to understand this distinction, since the notes mean different things and behave in different ways. What's more, they even seem to sound different in different contexts, even though they're literally the same pitch! See Piano Theory for a demonstration and further explanation.
Nearly all piano students make this mistake when beginning piano lessons. The clefs simply refer to pitch ranges, and they make it easier to learn to read music. The treble clef range happens to be higher than the bass clef range, but remember, either hand is free to play anywhere on the keyboard.
See the previous beginning piano mistake for an explanation.
This is an incalculable beginners' mistake, and it is not the fault of the student but rather of the teaching method. C major, which uses only the white keys, is actually the most unnatural key to play in since it does not fit the hand very well. The hand has three long fingers (the middle ones) and two shorter fingers (thumb and pinky). The black keys are not only raised on a piano keyboard, they are also shorter. The "rule of thumb" is that the long fingers play the short (black) keys, while the shorter fingers play the long (white) keys.
Remember this rule: Sharps and flats are not black keys, but the black keys are sharps and flats. A sharp simply means to play the next higher key on a piano keyboard, while a flat means to play the next lower key. That next higher or lower key may be black or white. All black keys are indeed sharps or flats, but a sharp or flat may also be a white key. E-sharp and C-flat are white keys, for instance.
When beginning piano lessons, remember that everything in music is relative. Have you ever tried to sing "Happy Birthday" to a friend, only to discover that you can't sing high or low enough? All you need to do is start the song on a higher or lower note so that all the notes are within your vocal range. You'll then be transposing to another key, say D major instead of F major. "Happy Birthday" can be sung in any key, and as long as you preserve all the relations between the notes (called intervals), it will still be "Happy Birthday." Try taking a very simple melody and playing it correctly, starting on different notes... and don't be afraid of the black keys!
It constantly amazes me just how many piano students, even moderately advanced ones, are unfamiliar with their scales. Scales are simply the notes of a given key, in order. Each scale has a proper fingering which is universal to all hands and which allows that scale to be played most easily. When you learn scales (and arpeggios, or broken chords), you're learning the fundamental building blocks of virtually all the music ever written. Not learning them is only a recipe for frustration. It would be like trying to memorize Shakespeare one letter at a time, and being totally unable to recognize syllables, words, phrases and sentences.
If you're just beginning piano lessons, watch out for these common mistakes! Good luck and happy practicing.