Yeah, definitely listening closely to vocalist. If you get the chance figure out the vocal melody to a song on guitar from ear. It will help your soloing a ton.

Also, listen to the over all structure of Slash's solos. Most of them are like a story: intro, development, climax, conclusion (w/ a signature lick to end). That's how you take a bunch a great licks turn them into phrases and turn them into a great and memorable solo that really grabs people. It actually has a lot to do with psychology. Having a good underlying solo structure gets into the mind of the listener.