Well this bit of the guide isn't very accurate, it must be said, here is how I got them, incredibly easy...
Flawless Fretwork 20
Score 100% notes hit as a Guitarist
This one is very easy, simply because every song on super easy is... well easy. For this one, I used Charlene and put it on Super Easy. One thing I noticed on Super Easy is, it gives you lots of chances for everything, but due to how the guitar works out, this is harder then the drums in terms of the tactics you can use. Just do a few re-runs but it's so easy on Charlene so don't worry about it.
Flawless Drumming 20
Score 100% notes hit as a Drummer
The trick to earning this one is quite straight forward. Play the song "We Will Rock You". Now use the buttons on the drum kit and go on Super Easy, this way the kick drum is done for you and the buttons ensure that you wont double tap a pad. Now what you need to do is build up enough star power so you can get a fill to activate it. On Super Easy it gives the chance for anything, so simply build up the star power, but DON'T use it because then it will keep giving you the fill to do, just miss it out and continue to hit the green and red notes.
With a little practice, this one is very easy.
Flawless Singing 20
Score a 100% rating as a Vocalist
Well I thought this one was going to be so hard! Turns out it isn't, like the guitar and bass, go on Charlene and go on Super Easy, the notes are so easy to hit it wont take long to achieve. Unfauntnatly like guitar you can't use the drum technique as you activate star power differently however with a few practices this is a piece of cake.
Flawless Groove 20
Score 100% notes hit as a Bassist
Charlene is very very easy on Expert, so Super Easy is nothing. There are only a few notes, nothing even close to being complicated.
Brian MAY Be Jealous 20
100% a guitar solo on Expert
Well this one is a lot easier then it seems, I personally find that the song "Swing Swing" by the "All American Rejects" is by far the easiest to do. Go to practice mode and practice the bit before the guitar solo and then the solo, keep repeating a few times to get the hang of it. I found this really hard at first but with about 3 or 4 goes in practice mode on 100% speed I went to do it, I missed one blue hammer on and I currently don't have it, but it is very easy and will only take a maximum of about 3 attempts if that.