1) Don't tell your future in-laws you have money without them knowing he's rich.
This never works out. The parents are poor, and they want money, but they didn't know they'd get it anyway. Sorry, you must die at the hands of your would-be-in-laws while your fiancee is sleeping and having a prophetic dream about your death. She seeks vengeance by law and has her parents executed. She probably got all the money, though, so good for her!
2) Use your brain! Don't go into the forest alone. Or without a man, unless that man is your brother. Makes sense, right? Well, if you go picking wildflowers in the woods with your sisters and run into a disheveled man who clearly has not bathed in months and is brandishing a letter opener, first of all, don't go near him. But if he sneaks up on you, threatens to kill you if you don't marry him, it's probably wise to do so because, look, he's gone and murdered you because you said no. Then kill him in his sleep later. But if the first two sisters manage to be killed, then you know what NOT to do, and you're also clearly smarter for not having approached the stinky man with a knife. But because you're brave, bold, and smart, you approach with your chin up and tell him he's your brother. He will LOSE HIS SHIT AND STAB HIMSELF. Works. Every. Time.
3) Don't trust your sisters. Don't even go anywhere alone with them. You're being courted by a fine young chap, but he hasn't quite fully given you all his attention, as your stupid sisters are trying to win him over, too. There is just too much hormonal jealousy over one man, who buys beaver hats for the youngest sister. For real, who REALLY wants a beaver hat? Maybe beaver gloves? I don't know. But don't trust a sister because she'll drown you the first chance she gets, she'll make instruments out of your decayed body. I repeat, do NOT trust your sister.
4) Don't marry a demon. Usually they come to you and woo you while your husband is at war. Then they pretty well convincingly tell you to leave your kids with your mom and selfishly flee with him to a snowy mountain island in the middle of nowhere. Where you'll never, ever, see anyone else again. And guess what, your husband was murdered by the demon, and your demon now-husband is hooved! Aw, hell! And you've actually died and you're now eternally with your demon lover. Sorry.
5) Don't get drafted in an overseas war when you're engaged, then immediately get engaged to another woman. Your former fiancee has joined the Navy as well under the guise of a man just to be with you. Little did she know that you were a gross jackass, and when she sees you in the act, boom. You're dead with a pistol shot lodged in your chest. IN THE HEART!
6) Know where the key is to your parents' house. Isn't this common sense? I mean Mary of the Wild Moor just knocked at her father's door as the bitterly cold howling winds muffled the sound. Not only did she die, likely of gross frostbite, her child died, too. If she had only known the key was under the rock by the front door...Bonus tip: Don't travel long distances by foot IN THE WINTER when 9 months pregnant.
7) Don't steal. You'll get executed, and your family won't want to save you, probably because you might've stolen from them, too. Your wife may swoop in at the last minute as the noose is around your neck. But I'm going to go ahead and guess that only happened once or twice in the history of hangings.
8) Never trust a guy that offers you "pleasures" to see, and it turns out he's just a drunken drifter who get a little rapey. Also, if you notice him digging a large hole, go on an run because he's digging your grave. Unfortunately you might just have to murder him because, Polly, listen, he's going to go to jail for murdering someone else and then lie and say it was self-defense. Then he'll just up and do it again.
So now you know how to avoid a folk tale murder! Good luck!