Dance Paradise

obviously this is an achievement based on skill, you can get this though any solo play - free play or career or a combo of both... i went though easy career to get a hang of the game mechanics and motor skills then did a run of the career on hard this time taking note of what rank i got in each song... then filling the gaps on easy in free play.

at the end of the song on the stats page in the top right corner there is a rank either amateur, apprentice, pro or star. (pro being lesser than star)

the score required varies, but if you've done two runs of the career you should have enough competency to at least get all pro... but to get all star rank you need roughly 9000 to 10,000 on most songs some will let you scrape though with 7000ish and it doesn't matter weather you play easy or hard.

easy while less moves means you have less chances to mess up a move (breaking combo) so really you can't miss more than 2 moves in a song.
hard with more moves going by alot faster you have more chances to mess up but you will need to have more focus

my other tip is to use star power only when you have a x4 multiplier and only to use it if it means your not going to mess the combo up... try and use it as soon as possible as even if you have two lots of star power you will only get one or one and half moves on x8