I've been picking fiddleheads for over 30 years now. Always along rivers and creeks. I cringe sometimes when I read inadequate instructions in mags and online.
Here is what I always do no matter how I'm using them. Clean and rinse well. Boil in salted water for two minutes. The water will be brown. Drain and rinse in cold water. Boil again for 1 to 2 minutes. The water will be light brown this time. Rinse well again. After that I saute them in garlic butter for about 5 min. and serve them with sour cream. I also make a fantastic cream soup with fiddleheads, wild garlic, mushrooms and green onions that is to die for. I freeze fiddleheads and leeks every year just for that soup.
Good luck guys. It won't be long now. Cheers