I've used all sorts over the years but the surgeons knot with the downstream tag-end left long works best for me. The number of turns used depends on the diameter of the tippet.
I start with a dropper length of about 4-6 inches which allows for at least one change of fly but keeps the length down to avoid snags. Distance between dropper(s) and point fly is anywhere from 12 to 18 inches.
When sight fishing, look over your shoulder from time to time, you never know who's behind you