As far back as I can remember I was trying to improvise breaks based on the melody -- starting especially when I was transcribing a lot of Stanley guitar -- George Shuffler, Bill Napier, etc, and its outgrowth, Larry Sparks. Learning the melody-oriented solos of others is one good road to finding the melodies.

Another thing I used to do a lot, and still do sometimes, is imitate a vocalist -- listening to Bonnie Raitt, or whoever, and trying to play a vocal line right after she sings it. Imitation in this way will help teach you to find what you hear. I also imitate people talking, or a baby making noises, or whatever happens to be in the environment.

Yet another way I was helped along was to play with a recording -- in my case it was often The Bluegrass Album with Rice, Crowe, etc -- and take all the solos, endeavoring always to play the melody but approaching it in a different way -- different octave, or bluesier, Sparksy, or more major-ish, Shuffler style, or Clarence-like. A recording is the most patient band you'll ever find. There were some days I'd spend an hour improvising on one song. I figure in about an hour a person could take fifty or sixty solos. There's a lot you can learn by trying to play that many solos on the same song, all in a different way.

A great melody-embellisher to listen to is Jerry Douglas. He's a master of stamping a melody with his own personality.