One of the easiest mistakes to make when playing the piano is to play a piece too fast before you have thoroughly learned the piece and therefore have the capability to do so. Most technically challenging and exciting pieces to play have fast passages in them and pianists dream of being able to play them to perfection. However, unless you are naturally extremely talented, the road to being able to play such pieces of music is a long and arduous one that requires a lot of patience.
The following steps should be followed when approaching the learning of a new piece:
(1) If you are more of a beginner, practice the left and right hand parts separately. Then when you have reached the point where you have learnt the notes sufficiently well, start playing with both hands together. If you are at a more advanced stage you should be able to start with both hands together.
(2) Learn to play the piece at a very slow pace, note by note, bar by bar and page by page. Determine the best fingering to use when playing with both hands together. Pay attention to the flow and dynamics of the piece and get to the point where you are able to play slowly and with ease without ever feeling out of control. Muscle memory is an important aspect to playing the piano. Your hands should be as relaxed as possible even when playing difficult sections and if you feel like you are losing control you are probably playing too fast, so slow down again. Although the natural tendency is to play a fast passage at a fast pace to begin with, resist this urge and instead play it very slowly, paying attention to the movement of your hands and fingers. If the fingering is awkward, attempt to find a solution that will be easier to play, or identify a way of shifting the fingering which involves taking your fingers off the keys rather than playing full legato (this may involve some pedalling work). This is particularly important for fast passages, as even if you can play them slowly, once you start speeding up the fingering you are using may prove a problem so you may need to make changes.
(3) As you continue to play the piece at a slow pace, over time you will have learnt all the notes and will be comfortable playing the whole work without unexpected pauses or feeling out of control. At this point you should be able to start increasing the speed at which the fast passages are played. However, take care to avoid ramping up the speed too much and losing control. The aim to be to gradually increase the speed as required while still feeling in control and not making any slip-ups. As time progresses (usually after some weeks or months for a long piece!) you will get closer to the point where you are satisfied with the final outcome.