Put down the axe for a while and listen to what you want to solo over. Hum, whistle or sing Lalalalalala along with it. The thing is to get used to thinking the tune you want to play. Jazz musicians talk of learning as much stuff as they can, and then forgetting all about it when its time to play. Practicing scales'n'such will develop some good technical skills, but to apply them, you need to develop your 'ear' as well. If you can 'hear' the solo you want to play, then you can teach yourself how to play it.