buldog5151bass
Kibble, milkbones, and P Basses. And redheads.
I don't think there are "rules". For three decades I began with my index finger on the downbeat, and regardless of staying on the same string or moving I would alternate. Last year I broke that finger, and spent months where I couldn't use it. Now I sometimes begin with index, sometimes with middle (we won't even get into the three-finger gallop).
Whatever works for you.
Whatever works for you.