This cheevo will be awarded for hitting more than 95% of notes in any solo.
Choose the lead career path and pick any song that has a solo featured in it.
This is far easier if the game believes you are new to the game as it reduces the amount of notes and spaces them out so its very easy to hit every note.
If the game has adjusted and solos are too hard I believe you can go into riff repeater reduce the difficulty and continue song and then the solo should be a breeze.
I personally did this on Nirvana in Bloom (was 1st song I played after loading up game for 1st time).