Jaco once said one of the best pieces of advice he could offer was to learn to melody of any song you can. The vast majority of the time we're so focussed on the bassline, on the drummer, on the next part of the song, on the pretty girl dancing in front of the stage that we forget to learn or even listen to the part of the song that everyone else listens to - the melody. Then when we're given something to improv out of the blue, we freak out and don't know what to play, so we tend to overplay or play something that is essentially a bassline with a modification that is nothing like a solo really. Kinda but not.
If we only took time to learn as much melody as possible, melodic phrasing would come a lot more naturally. Think of it as singing a song, but instead of your voice your using your bass.