There is some in the back of the magic book, but really focused on three-man teams.
Anticipate where the most likely upcoming decision is going to be. Ideally you are close (10-15 yards) and have a good angle--but choose angle over distance when forced to choose. The angle you want when players will meet allows you to see the space between them.
Get ahead of play (often), as that is what's coming next.
So much of positioning is necessarily learning by doing--this is also a place an observer can sometimes be a lot of help. For most refs, especially newer refs, there is a disconnect between their perception of where they regularly are and where they actually are. Someone watching can often give you tips relevant to what you are actually doing. I think you can do a bit of that, too, by thinking back to calls you weren't confident in--could you have done something different as to your position to have been better able to see the call?
