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One of the biggest problems is having too many choices. A good idea is imposing constraints or accepting already existing constraints. This can be very radical like using just one or two or maybe 5 notes and making something interesting with it (remember Beethoven or One Note Samba?).
What makes something interesting? A motif. It raises expectations one can play with: play what is expected or create a surprise.
Playing lots of notes tends to be rather uninteresting unless you want to make piano playing a sports game. Less is more. Develop, change register, play the same thing twice or half as fast, do it in octaves…