Each Blockstar is minted with a particular Ability level across a number of Attributes and each Blockstar has a maximum Potential across each of these Attributes.
When Blockstars are not engaged in an activity involving the entire Band (such as Recording) they are able to spend time Practicing some (though not all) of their various visible Attributes. Blockstars can Practice either individually (which improves just that Blockstar's Skills & Attributes), or as part of a Band (which also improves the Band's Chemistry, among other hidden attributes).
Practicing an attribute to level it up takes time, and the amount of time increases as a Blockstar gets closer and closer to its Potential Ability. At the lower levels that time could be minutes, but as the Blockstar gets closer to its potential, that time starts to get measured in days.
Attributes that can be Practiced are Musical Skills, Songwriting and Social Media. Visible attributes that cannot be Practiced (they improve with doing) are Gigging, Fame, and Promoting.
Some Hidden Attributes have a gameplay impact on how effective Blockstars are at Practicing.
The Practicing attribute has an impact on how quickly a Blockstar's practice results in a level up.
The hidden Concentration attribute has an impact on how long a Blockstar is able to practice in one sitting.
The hidden Patience attribute determines whether a longer practice session results in diminishing returns, or even a plateauing of progress over time.