This is my first time playing GH as well and it took a while for me to move from med to hard. Now I'm stuck on level 7 on hard... "3's and 7's" and "Before I Forget". I managed to get through "Stricken" and am too scared to try out "Knights of Cydonia", lol.
For me I put my thumb where the '2nd position' would be to hit the orange note and keep my fingers in the '1st position'. Whenever an orange note would appear I would slide up and back down accordingly, keeping my thumb at the 2nd position the entire time. This helped me learn how far to slide up and down. Now I don't need to do that anymore.