The plot of this poem is… er, there is no plot. And that's not just some Zen wisdom straight out The Karate Kid Part III. We mean, there actually isn't too much of a plot or really even an order to this poem. Most Blake scholars agree that "Auguries" is really just a bunch of different couplets Blake collected together and put into no particular order—aside from the beginning and the end part. There's a kind of overarching order, but it's pretty vague. So, are you ready for some vagueness? We definitely are.
The beginning of the poem is the key to everything that follows (like your Little Orphan Annie decoder pin): "To see a world in a grain of sand / And heaven in a wildflower / Hold infinity in the palm of your hand / And eternity in an hour." (Blake means that you can find universes of meaning and revelation hidden inside the smallest things.)
After that, some animals show up. And keep showing up. There are a lot of animals in this poem, and they're all being used to make some sort of greater point about the universe or human injustices or wisdom or… lots of stuff. Each one of the animals in these couplets is like that "world in a grain of sand." It's not just Pooh Bear fun-time hour—this is serious. Robins are being caged, atheist owls are flying around, roosters are getting ready to fight each other—and they all symbolize stuff and have greater implications. Not every couplet has an animal in it—some are just bits of sagely advice, some meditate on reason and doubt.
At the end, though, Blake's poem stops being so hodgepodge. He gets real spiritual, and discusses how God appears to people in different situations and what human suffering and joy are all about. He leads the reader through symbols ("auguries") pointing toward a state of spiritual innocence—a direct description of that enlightened state of being.