This is a great assignment! Your task is to think about how each road would attempt to attract people to choose it as the best path for continuing their travels.
The first road would probably focus on explaining to travelers that more people had chosen to use it. The road might talk about some beautiful sight that is hidden from view where the traveler stands right now, just beyond the place where the road "bent in the undergrowth."
The second road might encourage travelers to take it because it had not been used as often. This road might even beg people to use it, enticing them by pointing out that "it was grassy and wanted wear" and explaining that the traveler would have more peace and quiet along its route.
Both roads might conclude their sales pitch by telling the traveler that s/he could always return another time and try the other road, even though the traveler (narrator) "doubted if I should ever come back."