Note: This requires the official Power Gig guitar peripheral.
You have to hit 100% of the notes in any song with Power Chords turned on. Since difficulty doesn't affect this achievement, play on Recruit. The easiest songs for this are "You're Gonna Go Far, Kid" by The Offspring, "Again" by Flyleaf, and "Plush" by Stone Temple Pilots, so play one of those.
If you're having trouble with this achievement, try re-calibrating your game. Even if the calibration is only a few milliseconds off, it can really mess you up, especially when using the already somewhat temperamental official guitar peripheral.
This is a hard achievement if you don't have previous experience with a real guitar. If you can't get it right away, practice just hitting chords in general, then, once you're comfortable with that, switching between chords. If you devote a few hours to this general practice, then you should be able to get this achievement with significantly less frustration.