Beorn provides lodging to the company of dwarves, Bilbo, and Gandalf on their way to the Lonely Mountain. Beorn knows that their next route will take them through the dark forest of Mirkwood, so he offers them some helpful advice to speed them on their way.
1. Beorn tells them not to drink from or bathe in the stream that runs through Mirkwood. The water has a dark enchantment that will draw the user into a deep sleep. The dwarves do try to follow this advice, until Bombur accidentally falls in while crossing on the boat.
2. The travelers should keep to the path. This most important piece of advice from Beorn, and then again from Gandalf before he leaves, is ignored by the dwarves when they see twinkling lights in the wood and run off to try and find a party of elves. The elves disappear, and then the dwarves are lost in the woods, because they did not heed Beorn's advice, a foolish action which needlessly leads them into danger.
3. Beorn asks that the dwarves send his ponies back to him once they reach the forest. The dwarves briefly consider keeping the ponies, but decide it is probably best not to cross Beorn.