Guitar Hero II

Just like the achievement description says, you need to play and complete a song with lefty flip on, to activate lefty flip you need to go into the games options and change the settings there then go back to career/quickplay and choose a song to play, now it's important to note that the achievement doesn't require you to beat it on expert or anything, so if you're looking for a quick achievement just load of a song you like on easy and just match up the 3 colours which come at you slowly.

Of course there are other methods, for instance, you could place a mirror opposite your TV and play the song looking at the mirror so that even with lefty flip activated the highway will show the notes coming down on righty-flip.

I've linked in a video of someone playing on lefty flip so you can at least see how the notes should appear in left flip mode.

*^{Credit to b0b0l0gy for the video}

I found it easiest to do this either with my back to the TV looking over my shoulder or with a mirror propped on the sofa to flip the screen the right way around again.

I think the other two guides are okay but I also think Jayour wasnt too clear about activating lefty flip. Simply go to "options" in the game's main menu then to "video settings." From there you should see "Player 1 Lefty Flip," "Player Two Lefty Flip," (They have check boxes) and "Calibrate Lag." Go over "Player 1 Lefty Flip" and press A then back out.

Now In Quickplay or Career, pick a song and your difficulty. I recommend "Woman" on Easy because it's the shortest song in the game.

Left-handed people may not have a problem, but Right-handed people may to use that Mirror method like Jayour and Codehead UK said. If you dont have a mirror to use, just try your best. If the diffcluty is on Easy, its gonna be hard to fail the song.