Originally Posted by Folded Horn
How can I get better at passing notes, a melodic underpinning , and creating lines?
Sounds like you have a good ear...There are many ways to get to any destination. Knowing only what I read about you I might have you start by.... deconstruct the baselines by the players you consider your model. Analyzing them for the theoretical elements that Jazzcat refers to, and then simply recreate them changing one note at a time. For a melodic approach to creating practice starting on anything but the root, getting used to the sounds of the 3rds 5ths and 7ths as starting notes. Doesn't mean you would do this all the time, but it is a good exercise.
I would also have you create lines on one string for a while, then two, etc...
Then I would have you create lines that are always moving upward thru the scales and passing tones. Then downward, then mix them up.
All the while listening to the masters and learning their "ways". For me there are many, including Sir Paul, Lee Sklar, Chuck Rainey, Jamerson, Steve Harris, Sting, Pino, John Paul Jones, Will Lee, etc.. all of whom approach it a little (or a lot) differently.
It is impossible to put it all into an internet post, but that is one simple approach.
At Berklee we teach a lot of perspectives from different stylistic experts and include several classes devoted exclusively to bassline construction.