First, a necessary note: don’t eat anything you can’t positively identify without a shadow of a doubt. Some poisonous plants look deceptively similar to edible varieties, and certain other plants are only edible when prepared correctly.
Now that that’s out of the way, let’s talk about the fun parts of getting started. If you know nothing about local edible plants, the best thing to do is to figure out what grows in the area, what kind of habitat it likes, and when it’s in season. For example, if you’re looking for huckleberries in urban vacant lots in Texas during the early spring, you’ll be in for quite a bit of frustration. In Oregon’s forests in August, though, you’d have more than you’d know what to do it. It’s all about knowing where to look, and what you can expect to see.
If you’re truly stumped, there are resources out there to help. Fallingfruit.org maps out some locations for edible plants, though it’s crowdsourced and much of its information is imprecise or downright inaccurate. Still, it can give you insight into where to start your search, and what sorts of edible plants may grow in your area.
Be sure to check local laws for what you are (and aren’t) allowed to take. This particularly relates to plants growing on private property. It’s common sense that you wouldn’t go into someone’s yard to pick their carefully tended strawberries, of course, but what about those apples hanging out over the sidewalk on the limb of a tree that’s clearly on private property? In many areas, if the fruit is growing above public property (meaning the sidewalk), it’s fair game — but find out for your area specifically first.
Certain plants may have specific restrictions. For example, picking elderberries in California is questionable because the bushes are home to the Valley elderberry longhorn beetle, a protected species. Do your research and play it safe.
When you spot that gorgeous tree, branches heavy with lemons, apples, or peaches, it can be tempting to take as much as you can carry. Resist that temptation. Leave some for other foragers and for wildlife that may need it (remember that even in urban environments, there’s an ecosystem that depends on these sorts of food sources).
Once you’ve developed an eye for them, you’ll be amazed by how many foods are abundantly available even in cities.