If you want to increase your skill with an instrument to master level in Bitlife, you will need to practice and start taking lessons as soon as it unlocks at the age of six.
Every year following the start of lessons, you will need to practice by visiting the instrument you are taking lessons for under the Mind and Body activity tab.
Each time you take a lesson, your skill will rise little by little each year. You will also want to take at least one or two lessons every year, any more doesn't seem to raise your skills any higher, so it's not really worth doing more than two piano lessons.
Related: How to master the Piano in Bitlife
Do this every year until you finish high school, and you should master whatever instrument you are trying to master. Following these steps will also help you to complete this week's challenge that requires players to master the piano.
If you end up not mastering the piano, you can always take lessons by finding it under the Mind and Body tab again. But this time, it will cost you around 1k each time you want to do it, so it's ideal to do it at least once every year until you finish school at age eighteen.
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