Easiest is to learn from observing. You should play some 7K maps and try to put yourself as the mapper, giving reasoning on why you put such notes on that place.
Honestly 7K is too brutal for first-time mapper, but considering you know how to play mania, it's a good idea to observe some. Personally you want to know these: pitch relevancy (lower pitch goes left, higher pitch goes right), drum patterns (more drum sounds means more notes), and instrument mapping (tap for short sounds, hold for longer sounds).