I had some big trouble getting the hang on combo notes at first, but I watched that video linked above and used his macros on the shoulder buttons (although I did change so 4-note combos are on bumpers instead of the triggers because it felt better to me). It's all about learning the patterns they show up in. It takes a while to get the hang of it but after having gone through the first 120-ish songs on hard in the past couple of days (sorted by difficulty) I have pretty much gotten down the normal 2-note combos and the triangle shaped 3-note combos to the point where I barely have to think about what button to press.
I have not gotten to the combo notes that show up in a vertical line yet, so I still have some stuff to learn there but that's not something you will need to think about for quite some time if you just are starting out on hard.
But do watch that entire video, because it was
really helpful to me as a new player, especially the part about doing hold notes. That's the first thing you should really work at (unless you already are doing it that way) because it's gonna feel really awkward for a while. When I started doing the switch it took me a good second from pressing a hold note with my thumb, to pressing and holding a shoulder button and then letting go of the face button. Now it just happens in one quick motion, I still mess it up from time to time but I'm still a newbie in the grand scheme of things with my total of maybe 15 hours in the past week.
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Woo, second song I've managed to perfect on my sightread \o/
https://www.youtube.com/watch?v=Z-kXdVFDCoU
Perhaps not very difficult for all you people doing extreme songs, but I only have one week of experience with a rhythm game like this, so I have to start somewhere.
Only other rhythm games I've put any time into were Guitar Hero and Rock Band, and
they don't really help much in the gameplay department here.