Took out my bass guitar for the first time in forever, partially because I'd always been wondering how really good bassists usually do those pull-offs when playing walking lines, and why they are almost always on the G string. Turns out, pull-offs are quite easy to do (hence why some people overuse them), and are often on the G string (first string) because there's nothing beyond it to block your hand. It's much harder (though still possible) to do on the E, A, and D strings. This is coming from me, a noob bassist--I don't practice often, and it being my third instrument, I know the least about it. I can walk bass lines in good time (which I learned to do on the piano first when I was young, and surprisingly, it has translated perfectly onto the fretboard with little effort) but that's pretty much as far as my bass skills go.