for the instant answer; experience is your best teacher
it all starts with a commitment. back then, i always thought how i could create map as good as those people. it made me interested in mania mapping. i did (and still do) take a look on the editor of others' maps. figuring out how those could work.
the first step is being consistent. for example, a snare sound will be mapped into a 3-note chord, 2-note chord on kicks, and a long note on synths and pianos. your ability will build up slowly from that point. keep in mind that playtesting does an important role on this
nothing goes instantly. you can compare between my first map and my latest map on my beatmaps part of my userpage to look how two years of experience can bring you. never be afraid on trying out something
good luck!