There are some old threads on this - try a search.
The main points seemed to be that it was a very rewarding role, but much more to it than perhaps meets the eye, as obviously the ceremonies are matters of important legal record. I think that you trained in one side eg. deaths, then gradually expanded your role to marriages and births.
There is obviously a very sad side to it, so you need to be able to handle families very professionally and compassionately.