Happy you think this is a good contest. We're glad to see it well received.
There are certainly plants that ARE NOT good to eat. Take water hemlock for example. It's up where we are and is quite poisonous, even looks ever so slightly (although way bigger) than queen Anne she lace (aka wild carrot).
The best idea would be starting with easy to ID plants that don't have any harmful look alikes. Pine needles and dandelions for example. Take a look at some resources for easy IDable plants where you live. Violets are a good and tasty choice for this. Chickweed too. Best luck