Doorbell. Wait for 30 seconds to a minute and ring again. If there was no doorbell or it wasn't working I did a moderate knock.
Since I wasn't awake back then and thought I'd be bloodguilty if I just pretended, I did make a good faith effort, but at the same time knew how startling and annoying it was when someone came to my door. Like most JWs, I didn't want to be there either and was hoping nobody would answer.