I'd say the best (and safest) way is to find a local mycologist or foraging group and try to sync up with them. Barring that, see if there are any good guides specifically for your area.

As a desk guide, rather than an in-the-field guide I'd recommend "Mushrooms Demystified": https://www.amazon.com/Mushrooms-Demystified-David-Arora/dp/...

Start with the definitive reference: http://www.amazon.com/Mushrooms-Demystified-David-Arora/dp/0...

Take a class or find a friend who is already knowledgeable. Or you could try getting in touch with culinary foraging folks. You'll quickly find out that there are only a few species of mushrooms that people tend to forage for, and there are fairly easy ways to tell the good ones apart from the potentially dangerous ones. There are also only a handful of truly deadly mushrooms, once you have familiarity with both sets it becomes a lot easier to trust eating something you find out in the woods. Generally, avoid the "stereotypical" looking mushrooms (the "little brown mushrooms" and toadstools), and stick to the most distinctive and easiest to avoid confusing edible fungi.