As someone who's been mapping for 7 years and counting (though with no ranks, probably my own fault), I can tell you that's all dependent on what you're looking for based on your definition of "good" maps and mapping. Aesthetics is definitely a goal for all mappers looking for rank, though few do it while maintaining difficulty and representing music.
What's really best is just playing some maps, and actually copying the style of maps that you take a liking to. Not copying and pasting the map (don't be Sotarks who copies from himself and seems to "influence" himself), but taking certain ideas of how music is represented through placement of objects, what patterns people choose, circles vs. slider choice, how they deal with odd rhythms, how do they indicate different sections like slider velocity change and extreme spacing, what parts are consistent and what parts have different representations, and how they emphasize certain sounds and parts of a song. New combos could also be an influence. Do you NC based on the song, based on the objects, or based on the rhythm within the song?
I don't think that's necessarily a bad thing as all mappers had to have been influenced by someone else to a certain degree, and by copying, you also create your own style of mapping because you're eventually disagree with certain representation of music and want to branch off from what one players might do, either thinking your own version of representation, or even taking another player's idea in place. Sooner of later, the many influences of different mappers alongside your own ideas become one concrete style.
Think of mapping like fashion. If you like an article of clothing, you'll buy it. If you don't, you'll buy something else or you'll sew something for yourself and make altercations.
I also heard that playing rhythm games helps. Games that don't have that traditional rhythm game up-down columns or require the players to look ahead to see incoming objects like NOSTALGIA, Beatmania, or Pop'n Music, tend to be good because they not confined to vertical lines of objects. Something like jubeat (that's all I know) uses squares, almost in a similar fashion to osu, actually, to represent music. I think fanzhen0019 gets a lot of inspiration from there.
The hardest part of a map for rank, however, tends to be the idea of playability. If you're looking to make difficult maps, the topic of "playability" will come up a lot simply because people have different ideas of what is playable and what should be considered rankable since everyone has different levels of skill on osu. Especially in the higher difficulties, there seems to be much debate of what is playable, since these kinds of things aren't exactly set and stone in the ranking process. A lot of this will come when you discuss with BATs and NATs since they're the ones that have the power to rank and disquality maps, but with regular players as well. So, the idea of playability is really based on the public reception of a map.
This is my take, and I'm sorry if it's a bit choppy.