When you're building a solo, you can use various scales (major, natural minor, etc..) to help find the notes that *you* would like ot hear in the solo. If you're ever really stuck on a solo then try using a riff from a popular song (to add a comedic value or something to the solo - to further drag the audience into the piece). You can play Britney Spears' "Oops I did it again" to lead off a solo, or play the "Freebird" (Lynyrd Skynyrd) solo before going on to something totally different (completely you).