I have been playing for 25 years on and off but I am constantly learning as guitar has many diferent approaches.
The key to a great solo for me has been to build up an arsenal of modes/scales and riffs. Practice them so they are committed to memory.
And then when playing shut your brain off, listen and feel the music.
This is where the magic happens at least for me.
Thinking is the death of music, therefore learn as much as you can so you do not have to think while playing.
The links for the lessons from Chris S that are in the body of this post are some of the best lessons here and are great to study. I find myself going back and rehearsing along with these fundamental lessons. Not to mention he has some really incredible speed and great teaching technique.
Cheers,
Jeff