Two roads diverged in a yellow wood (1)
From the very first line of the poem, we see a man confronted by a choice in nature. Though we suspect that this choice is actually a metaphor for a choice in his life that includes other people, and not just the natural world, we remain in the natural world for the majority of the poem. It's a nice breather in the forest, away from the hustle and bustle of people and cities – which make our choices so much more complicated.
And looked down one as far as I could To where it bent in the undergrowth (4-5)
Well, unlike we thought in the first line, nature can actually make things complicated. Even though we are in a peaceful forest making our choice, it's a little intimidating that the bushes and plants of the forest are keeping us from seeing where the path we take is leading us. Looks like we're stuck; in the natural world, and in civilization, we can't always see where our life is going, which, when it comes time to make big decisions, is no fun.
And having perhaps the better claim, Because it was grassy and wanted wear (7-8)
Now we see the speaker's bias towards the natural world. He thinks one of the paths is better, because people haven't traveled it as much. The natural world as close to its original state as possible is preferable to our speaker. He seems like a bit of a loner.