Given that buses can be crowded, I thought I'd share our experience with catching a bus in Amalfi to go back to our rental home, which was halfway between Atrani and Minori. We bought the tickets in the tobacco shop at Amalfi's port, right across from the line where everyone was queueing up waiting for buses. The buses run on a schedule and we were going to have a ten minute or so wait. 100 or so yards away was a spot where a few buses were just parked. Some had drivers in them. My husband suggested we go over there, find the bus going our way, and ask to board. I said no, we were clearly in the right place to wait for the bus. When one of those parked buses finally started moving, we could see that it was marked Salerno, which was the the right bus for us. However, it drove right past the line of waiting people without stopping, already completely full of passengers, apparently people who did what I had nixed. Other people in the line were as surprised and disappointed as we were that the bus didn't stop. We made inquiry as to how long we were going to have to wait for the next bus and it was over an hour so we just walked. The next day, again in Amalfi, and again wanting to catch a bus home, we boarded in the bus waiting area instead of lining up at the bus stop. The driver had no problem letting us on, and many people were doing this.
In Ravello, there is a short tunnel (for traffic, with sidewalks for pedestrians) between the bus stop and the entry to the town's main square. When you are leaving Ravello, buy your ticket at the tobacco shop or kiosk (I forget which) that is right before you enter the tunnel.