Does successful mean that you hit the right notes more than 60% of the time??
Well... Jim HALL has a sign in his guitar case that goes: "make musical sense". What I do is try to get the best melody I can hear in my head at the moment that I start my improvisation. Then I'll take it, develop it, repeat it, answer to it, answer the answer... That's what a solo is all about, not linking licks one after another. That's what makes your solo unique and personal. I am always a little disappointed when I see that guitarists play their CDs solos note for note! Of course, there are tunes that were written for this (I'm thinking about 'for the love of god' by Steve VAI, that allows little freedom) But as a teen, I enjoyed listening to guns and roses because Slash would start his solo pretty much like the disc's, then he'll take off, and maaaan, that was awesome...