When mixing, musicians will play certain sections softly and others with more force to put more emotions into a performance. This is what we call the dynamic range. Dynamic range is a tricky part of mixing since you have to decide whether to reduce or expand it at the same time maintain natural dynamics.
Before anything else, you should consider the genre and the listener. In mixing pop music, strive for polish. The vocal is almost always front-and-center, the kick and bass always powerful, and supporting elements need to be as tight as possible.
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