DanceMasters

A song I would recommend for this is Still In My Heart. There is minimal foot movement, and what movement there is is stepping back and forth. Play through it a couple times on STANDARD to get the stepping down and then you can play it on EXTREME and only concentrate on the hands. There are a few tricky parts with the hands that will take a little practice but I got this achievement done in around 30 minutes from just playing the song over and over until I got it down.

From what I have gathered, the AAA rating doesn't depend on score so much as the amount of Perfect, Great and Good Combos you have, as well as misses. I scored 470k on one run with like 7 misses and A ranked it and I scored 430k the next time with like 2 misses and I AA ranked it. You probably won't get AAA until around 550k but I'm not quite sure how this ranking system works, so just try to get a run through with minimal misses. Unlocking the Secret Ripples before hand would increase your score, but I didn't do this so it is not necessary.

Also, a useful bit of advice would be to try to perform the actions a little bit earlier than the dancer on the screen. Doing this, I was able to get Perfects most of the time, especially if you're having a hard time hitting the sweeps (the arrows that you follow with your hands and feet). Apparently the game expects you to kind of know what's coming before it comes, which makes no sense to me.