Never really believed in any of these, but anyway:

A variant on the "eat the crusts" theme: if you eat burned crusts, you will get a good singing voice!

You will catch polio if you play with fallen autumn leaves.

Breaking a mirror will give you seven years of bad luck.

There's an ugly goblin living in the well, and he'll catch little children, so don't go near.

If a girl picks seven different flowers on Midsummer's Eve, and puts them under her pillow, she will dream of the man she is going to marry. (Special for Sweden, I believe.)

If you sing and make noise before breakfast, you will be in trouble before nightfall (originally: in a hawk's ass. My Mom's saying. She couldn't explain exactly how this would happen.)