Learn What to Avoid
The only thing worse than a dull nature walk is a red, itchy one.
Knowing what to avoid is at least as important as knowing what to seek out, especially if there are little ones getting up close and personal with nature. Any great nature walk, backyard or otherwise, is preceded by a brief lesson on how to recognize poison ivy and poison oak.
A book or the Internet can make it easy. Google "identify poison ivy poison oak" to see countless options, or check out the library's supply of plant reference books. Just look at pictures of the itchy stuff and perhaps do a little flashcard-style quiz before heading into the yard.
If you're sure your yard has neither of the lamentable growths, meaning you've done a close and recent examination of the entire space, corners and all, you could probably skip this step -- although really, what harm can it do to learn to identify some plants? Especially ones that could ruin another, future hike?
And speaking of avoiding trouble…