Hammer Ons and Pull Offs are excellent ways to nail solos. If you see a note with a smaller note coming up after it, that indicates you can Hammer On.
For guitar solos (where the background for the notes turn blue and a percentage meter appears) on the Fender Stratocaster guitar only, use the Solo buttons (the small ones near the body of the guitar). Instead of strumming, simply tap the buttons as the note passes the bar. This making solos with many notes very easy. Note: You may want to use the included guitar strap to keep one hand on the regular fret buttons and the strumming hand on the solo buttons.