I think we have had enough of the multiple bad guides for unlocking this achievement.
So here's my in-depth guide on how to unlock this achievement. I will go through all the steps I did. This guide will make sure you unlock this achievement!
1. Make sure you have played a few songs in "Career Mode" by yourself, and with a few friends on Xbox Live.
2. Play a few songs in "Quickplay" by yourself, and with a few friends on Xbox Live.
3. Play each of the online "Competitive" game modes, which are:
-Pro Face Off
-Team Pro Face Off
-Team Pro Rockfest
-Band vs Band
"Some people say you only have to play a online 'Band vs Band' match, and you can do skip the rest and go to step four."
But just in case do all of step three, it doesn't take long anyway.
4. Get three friends that play the same instrument as you are currently playing and invite them to your "Competitive" party. After they are in your party, press start instead of the orange fret that you use to look for matches online.
Alternative: You could also hook up four of the same instrument and sign three of them in as guests. If you do this there is no need to invite three friends.
5. This takes you to a list of game types. Play them all, the team ones and the non-team ones! With the exception of Band vs Band, I didn't need this to acquire the achievement.
6. If you don't have the achievement yet go in and play some more Rockfest or Team Rockfest online, that might help. Just to be safe I would play all the online game modes at least twice.
When did my achievement unlock?
Well I was stuck, couldn't get it to unlock, I played all the online match types, and I played Rockfest and team Rockfest a thousand times.
My solution was to invite three friends and do what I said in steps four and five. My achievement unlocked after I went through that list with three of my friends!
Here is a complete list from ssmaster69er's solution, thank him:
Band vs Band
Team Pro Face-off
Do or Die
Team Do or Die
You don't have to WIN any of these matches not even the elimination matches, I let my friends win them all when we where boosting and it still unlocked. I didn't even hit notes most of the songs we did, so you can chill and cook some corn dogs while the song is playing!