Following on from Rumncoke's posting, I used to sing ballads ( by request, may I add) to my two sons instead of bed-time stories. They particularly liked Lord Thomas & Fair Eleanor - they never tired of him flinging the Brown Girl's head against the wall. They also loved the elder sister ( who had just drowned her beautiful younger sister Kate ) getting away with it by putting the blame on the miller who was hung at his own front gate.
Coming back to Crow Sister's initial posting, how does one take on the big ballads? My way - and I am not in any way being prescriptive, but just saying what I do - is first, find a good story that you REALLY want to tell other people. Second, find a text version that you like - add or subtract verses to make it YOUR way of telling the story. Third, find a tune you both like and can sing without worrying about. If you are constantly worrying about pitching the notes it won't make for easy singing and the story is paramount.
After you have selected your version, learn it so it becomes part of you. Like many other posters here, I see the song in pictures in my mind's eye.
Then sing it to anyone who will listen. And don't fret about people who say audiences get bored. You can bore an audience with a one-verse song if you sing badly. You can engage an audience with any song sung well, but you must believe in it.
Mary