Clear vocals usually need presence, not volume — a boost in the right frequency range does more than simply turning the whole track up.
A boost of 2–4dB around 2.5kHz is the classic move for vocal clarity, since that's where consonants and articulation live. If the vocal also feels thin, a small boost around 500Hz can add body back without losing the clarity you just gained.
If a vocal sounds harsh rather than unclear, boosting further will make it worse, not better. A small cut around the same 2.5kHz region can resolve harshness while keeping most of the presence intact — always check which direction actually helps before committing.