Rock Band 3

Low Rider by WAR is the best song for this. Set it to easy difficulty and put one finger (suggestion: little/pinky finger) on the 7th fret of the first string, and another finger (suggestion: index finger) on the 5th fret of the third string down (I do not know what the names of the strings are in terms of lettering but you will know which ones I mean if you have ever used the pro guitar before) This pattern is consistent at a slow pace all the way through the song. As long as your fingers are comfortable, you should be able to get this without moving your hand or without any difficulty whatsoever. In my opinion, this is the easiest song in the game.

If you are like me and play the guitar by the sense of touch, and therefore are struggling to play the third string without making a mistake or looking down, run your fingers slowly over the second string. Use the sense of touch to guide your hand into the right position. I five starred this song first time with 94%. Good luck!

The best song for this by far is Du Hast. Every note is on one string. Set it to easy and try not to miss a note, I got flawless the first time I played through this song and the achievement popped about halfway through the song, if I remember correctly.

If you can't play Du Hast on easy, then put up your Rock Band 3 for sale on eBay because you have a long way to go.

The best way for those like me who aren't so great at guitar, Play "Living In America" by The Sounds on Easy, as it is the easiest song in the warmup list. All of the notes are on one string but 2 that are on the smallest E string Fret 4. Just try your best to get a multiplier to 4X, Then activate overdrive. Voila!! Achievement should pop at the score summary.

You need a Pro-Guitar for this.
It doesn't matter what song you select on Pro-Guitar, or difficulty, as long as you get a streak of 30 notes so you can bring the multiplier up to x4.
It does not work if you get a x2 and then use Overdrive.
Pretty simple on "The Hardest Button to Button".