For the most part, trying to earn five stars on all songs for the Constellation Maker trophy is what brings this difficulty rating up to 3-stars. It's not just a question of being an awesome dancer, but having the perfect lighting and some luck with the Eye Toy picking up your movements, as people can have problems with the motion detection.

NOTE: You will need a minimum of 2 Move controllers, as well as two players, for this Platinum.

This isn't really a game which requires a road-map. But if you really need some sort of direction, we recommend working on the Just Sweat mode to rack up those points and work towards the Sweat Me A River trophy. Make sure to set up a 7 Day Workout Session in order to keep track of your Sweat Points. As you work towards earning 30,000 points, you'll be unlocking other trophies as well.

Once that's finished, you can start working on the Constellation Maker trophy, which requires getting 5 stars on every choreography in the Songs tab. This is probably the most difficult trophy in the game, and you may have to mess around with the lighting in your room if the motion detection isn't in your favor. Also, try wearing an outfit that's a different color from whatever's behind you, so the camera can better track you.

If you managed that, then congratulations! The rest is simply mopping-up whatever trophies you're still missing. For the Big Band Theory trophy, it's possible to unlock this with only 2 move controllers, if each player dances two parts, such as to I Was Made For Loving You Baby by KISS.

Here's a useful Trophy Guide, by bio551:
http://www.playstationtrophies.org/game/just-dance-3/guide/

And Josh Romero has a few useful Trophy Guide tips, here:
http://www.videogamesblogger.com/2011/10/04/just-dance-3-achievements-trophies-guide-xbox-360-ps3.htm

Here's a Track List:
http://www.joystiq.com/2011/08/19/whats-this-its-just-dance-3s-latest-track-list/

Lastly, here's a basic Trophy List:
http://psnprofiles.com/trophies/1220-Just-Dance-3-