To unlock this achievement you must complete every single mix / song, doesn't matter what order. Just complete them all with a five star rating or higher and the achievement will unlock. You must five star all of the dj / guitar setlists as well!
Here are a few tips that will surely help you unlock "The Grandmaster!" achievement in DJ Hero.
Just to inform you, the two songs below are probably the two toughest songs in DJ Hero's setlist. That is if you're playing on the medium difficulty. Groundhog by Noisia is still the hardest song overall in the game though. If you can beat these two songs on medium you should have no problem with the rest.
1. Groundhog by Noisia
2. Monkey Wrench / Sabotage by Foo Fighters / Beastie Boys
[Read below for more tips, if you are still struggling to complete the medium difficulty.]
Now here is a little tip that will "HELP YOU OUT" a lot if you're not very good at this game, because the song Groundhog by Noisia is "CRAZY" with the crossfader and can be very challenging. (That is, for us that are not godly at DJ Hero; I have a secret to share!)
All you need is a friend who is decent enough to know what's going on to move the crossfader back and forth for you. So, have him crossfade and activate euphoria for you when necessary. While they are working the crossfader, you must do all the note tapping and scratching. This works really well for a few of the harder songs on medium. Just grab a friend and give it a try, it's far easier than it sounds!
Hope this helps, have fun scratching. :)