As far as learning/writing...everyone has a different approach. I'll learn a cover tune before practice, but perhaps there's something in the bass line I've missed? (We cover a lot of old rock, with bass lines buried *deep* in the mix.) Or maybe the guitarist is playing a passage wrong, and he needs to be corrected, or whatever.
As for originals, since the guitarist writes them, we have to rely on him to bring them to us. We record them on a video camera, and then we write our own lines to them, using the video as a tool.
Our drummer, we have discovered, really *needs* to be directed closely when working out originals. He's just not that good, yaknow? If we have to do that in front of people, he gets very defensive. BTDT...his cousin used to come hang out all the time at practice. I voiced my preference that he not come over until we are done, but was ignored. Until we had to correct our drummer in front of his cousin, and the drummer became angry and defensive.
So...I got my way. No more audiences at practice.
Cherie