The game automatically sets your lives to "5". Start the game on Easy/Arcade. This only works on the Easy difficulty playing Arcade mode. (Hard difficulty is missing one point-awarding move [the first whirlpool in the Raging Waters scene], so you can’t get a perfect score playing on Hard. Home mode is also missing the first 49 points awarded in the game [most likely it will be the Crumbing Vestibule scene]). It doesn't matter if the move guide, move beeps or the arcade monitor is on or off.
One word about the Falling Circular Platform scenes; there are four different versions of this scene (a 3-ledge and a 9-ledge, each mirrored/reversed, making four scenes). To get a perfect score, you must jump off the platform at the last possible ledge (either 3 ledges or 9 ledges) to get the maximum amount of points. Use the strategy described in Going Down to see which scene you are on.
Another note about one other scene that could screw up your score: the Snake / Mist Room. The correct moves (according to the move guide) are , , and . You can bypass the third input and press instead, but you will miss out on 49 points (which is necessary for this achievement). So, when you get to this scene (the one with the red/black/white snakes), make sure you input FOURmoves, not three.
Save at the beginning of every single scene, so in case you die, you can just reload that save. You have to make it to the dragon's lair without dying.
You shouldn’t have died at all by the time you reach the dragon’s lair. When you do reach it, you should have 288,494 points, and when Dirk says "Wow", it quickly adds another 49 points to your score (for starting the scene, making your score 288,543). Many people think that you reach the dragon’s lair with 288,543 points, which is false. The points get added very quickly so it seems that you start the scene with that amount of points. If you have less than 288,543 points after Dirk says "Wow", then you won’t get this achievement. Save your game at this point if you have the required points.
Play through the scene as normal, inputting the correct moves. When you get to the final move (pressing to kill the dragon), don’t press it. Purposely let the dragon kill you. Do this a total of four times. Save your game each time you start the scene with one less life. On your last life, kill the dragon. If you die a fifth time, simply reload the save and repeat the final life.
When you reach the Dragon's Lair for the first time, at the very beginning right after Dirk says "Wow", you should have 288,543 points (5 lives left). Save the game.
After your first death, after Dirk says "Wow", you should have 315,338 (4 lives left). Save the game.
After your second death, after Dirk says "Wow", you should have 342,133 (3 lives left). Save the game.
After your third death, after Dirk says "Wow", you should have 368,928 (2 lives left). Save the game.
After your fourth (final) death, after Dirk says "Wow", you should have 395,723 (1 life left). Save the game.
On your final life, when you defeat Singe, you should have 427,469 points and the achievement.
The reason for this is when you die, you start the scene over again, and you accumulate all the points again up until you are to slay the dragon (which in itself is worth 5,000 points). If you were to kill the dragon with all five lives left, you would end the game with only 320,289 points. On each of your four lives, you get an additional 26,795 points (for all moves excluding 5,000 for slaying the dragon), so 26,795 times 4 (lives) equals 107,180, plus 320,289 equals the top score of 427,469.
If you saved your game when you reached the dragon’s lair (with the appropriate score), play through it without dying and slay the dragon to unlock Flawless. Then, just reload the save and do what is explained above for this achievement. That way, you only need one playthrough on Easy for the entire game.
You can earn this achievement only by using a controller.