Let’s use my own childhood as an example. I heard a few too many nursery rhymes from my crib, like “Mary Had a Little Lamb” and “Merrily We Roll Along.” Songs that focus on the 1st, 2nd, and 3rd scale degrees, small intervalic jumps, feel more familiar, more comfortable, and more nostalgic, to me at least.
The specific frequencies you choose to boost will vary from track to track, and especially from genre to genre. It’s common to apply a subtle boost on the high end using a gentle shelf, typically around 8 kHz or so. So be sure you don’t bring back any of that nasty sibilance — and be careful boosting between 3-6 kHz, as it often causes the vocal to sound shrill and harsh.