Although there are countless pieces of music out there, there are some general habits to keep in mind that all professional musicians have in common and will help you sound professional as well!
Through my own studies, observations, attendance at numerous conventions, masterclasses, and consulting with other piano teachers both locally and around the world, I have complied this list of what I call ProTips - 20 tips from professionals to sound professional!
The 3 Core ProTips
With few exceptions, we always want a clear tone, regardless of the dynamics. Even in the softest sections, we still look for clear tone and phrasing (unless we purposely want to blur notes to create an effect). Also, consider projection as it applies to the venue that you are performing (small practice room vs. larger concert hall).
Also known as "musical sentences," phrasing involves a natural rise and fall to each phrase, often involving tempo (rubato) and dynamics (crescendo and diminuendo). With few exceptions, no two adjacent notes sound the same, as to keep a constant sense of phrasing. Singing (even if you're not a vocalist!) can help with understanding of this greatly as pianists are not often concerned with breathing (except to not fall off the bench)!
Since pianists are capable of playing multiple notes simultaneously (one of the awesome strengths of pianists vs. other musicians), we have to know which voice(s) to emphasize. Where is the melody? What do we want our audience to hear? For more basic pieces, this is usually melody vs. accompaniment. But for more advanced pieces, there is a "hierarchy of voices" in which different voices have different levels of priority. First the melody, then the bass line, then all the inner voices very soft!
4. Confidence & Stage Presence
This is necessary of all performers, not just musicians. By believing in yourself, you project it onto others and captivate the audience through your connection with them. And this doesn't just apply to when you are at the piano, it involves all interactions with the audience, including walking on and off the stage and bowing!
5. Musical Expression - Make It Personal
Although many people throw around these terms a lot, what does it really mean? For a quick fix, phrasing is an effective way to make the music sound more expressive. However, getting deeper than this is much more -- it has to be personal. If it doesn't evoke a reaction in you, it certainly won't with the audience. Where are the composer and performer trying to take the listener?
Forte sections vs. piano sections. Staccato vs. legato. Dramatic vs. lyrical. "A" Section vs. "B" Section. Contrast makes music interesting, otherwise it all sounds the same!
Listen to performances of others -- both professional and amateurs/students. Both groups will give you ideas of what sounds good to you, and perhaps what does not. Blend these together to create your own unique interpretation.
Listen to yourself
Record yourself -- you'd be surprised how differently you sound when you're just listening and not playing.
Listen as you play -- this is important to adapt to the acoustics of where you are performing, both in regards to the instrument and the acoustics of the hall. Don't just "copy and paste" what you do in practice when you go out to perform
Listen to other genres -- always keep a fresh perspective and expose yourself to new music! It will give you new perspectives on what you are learning
8. Get in the Composer's Mind (Analysis, Chunking/Patterns)
Music theory to the rescue! It is not necessary to analyze pieces to be able to simply play pieces, but to get the full understanding and appreciation, it is essential. It is like cooking. It may take just a couple of minutes (and doesn't take skill) to eat a slice of pizza or a fancy cake, but to understand all the effort that goes into making those gives you a much deeper appreciation. Composers always write with intentions and patterns in mind, music is not random. So go and figure out what those are!
9. Freedom in Movement & Circular Motion
There is often much tension in musicians (and I'm not talking about musical tension). Physical tension abounds, even in professional musicians. All energy should be able to flow freely without kinks, and nothing forced.
10. What is the story?
The most common first question in masterclasses is either "What is the title of this piece?" or "Who is the composer of this piece?" Knowing the history of the piece, and what you are trying to achieve is essential as music communicates with the audience.
Resist the temptation to just learn the notes and apply fingering later. Poor fingering habits are one of the most difficult things to change when you've already practiced a piece and it will show when you try to play a piece quickly!
12. Large Dynamic Range
The piano is capable of very loud and powerful sounds, and the most delicate. But you have to make it happen! It takes great technique to produce sounds at both ends of the spectrum.
13. Sense of the Beat
Even the most lyrical pieces with lots of rubato still have a fundamental beat. Just like a heartbeat, the beat can speed up or down, but must remain consistent. And keeping the beat is not simply playing notes at the right time, but knowing which notes and beats to emphasize (which varies from classical to swing, for example)!
14. Attention to Score
There is a lot written into the score. Make sure you follow everything -- particularly dynamics and articulation! This is especially fundamental if you are taking part in examinations or competitions. Studying the score away from the piano has huge benefits.
15. Musical Style & Interpretation
This is a tricky one. How do you play baroque vs. romantic vs. ragtime vs. new age? This is where musical knowledge and understanding really comes into play, as you navigate through different genres of music. Virtually all musicians spend entire lifetimes in contemplating how to play in these different styles.
More Advanced ProTips and Considerations
16. Visual Aspects
A few pianists have been able to produce the best music with stoic facial expressions and music, but it is much easier (and enjoyable) to relate to someone who also visually matches the music they are playing. Body movement and facial expressions, in reasonable amounts, can enhance a performance greatly.
17. Pedaling (Color & Harmonics)
Basic pedaling sustains harmonies, but advanced pedaling is so much more, including to add color, contrast, emphasize certain notes, and for harmonics. Advanced pedaling also includes usage of una corda and sostenuto pedals and techniques like half pedaling and flutter pedal. How to pedal can also depend greatly on the venue and instrument.
Already mastered your piece so you can play it in your sleep? Now try playing it a whole step higher... this will see if you've really "mastered" it!
19. Improvisation & Arranging
Playing the same section over and over 100 times from uber slow to performance tempo 10x perfectly is one method... but can result in a stiff performance, even if it is technically accurate. Improvisation and arranging on the piece that you are practicing requires a clear understanding of what the composer is writing, yet allows the performer to stay fresh and experiment with different
20. Inspiration, Appreciation, & Humility
And finally. Remember why you are doing all of this in the first place. It is so easy to get lost in all of the details as listed above (which is why musicians are so awesome!), but fatigue can set in. Remember that great performances can (re-)inspire others! Please make sure to appreciate all the people that support you, including the audience as well as people close to you. And remember to stay humble. Self-confidence is important, but there is always a place for humility, and you will gain so much respect for it.