If you're having trouble getting this, here are some tips:
It may sound cheap, but PAUSE and get ready for every single measure. Pausing the game brings up a menu which only covers up a small portion of the left side of the screen leaving the measures in clear view for you to look at 90% of the time. Time to stop and think is a great commodity in this game.
Also, use your SHIELD. If you get to a part where you don't think the pause trick will get it done, tilt your guitar to hit the shield. This will keep enemies from hitting you which will break your combo, you just have to make sure you don't make any mistakes in this time, as that WILL break the combo.