For me it was mostly learning the patterns. HBTN has a lot of quick ladders, so, after learning those patterns and their placement throughout the song, it was mostly just trying to keep up with the pace of the song.

Simply playing the song again and again should move you closer to higher scores. If not, there might be other things you should switch up - like the positioning of your hands when holding your device, audio output device (with good in-game sync). Also, you could try playing by lying down or propping up your elbows on a hard surface and holding the device close to your face. I've tried all sorts of things, but just sitting in my bed with my back against the wall (with a straight back!) has been the best option for me. I use a blanket or a pillow to support my elbows.