Pokémon Red and Blue/Route 9-10

'Using Cut, chop your way to Route #9 from Cerulean City. Check into the Pokémon Center near the entrance to the Rock Tunnel, then plunge into the underground passage. It emerges on Route 10, a very short route to your next destination, Lavender Town. This might seem like a roundabout way to get there — but it's the only way.'

Route #9: before the Rock Tunnel
The trainers here are abundant, but many of them can be avoided (only need to battle two), and there's a Pokémon Center at the end, in Route #10, before you go into Rock Tunnel (A on the map). Make sure you teach Cut (as HM01) to a Pokémon that is able to learn it.

Above Trainer #1 on Route #9 is a ledge with a tree on the right side. You'll have to go around to reach the tree, but examining it will net you an Ether.

To the left of Trainer #2, there is TM30. The TM contains Teleport, which allows you to escape from wild Pokémon battles; the move always fails to work in trainer battles. It can also be used outside of battle, where you can warp to the last place you healed (which can be a Pokémon Center or the player's house).

Before you enter the tunnel, hack aside the top bush and search the rock face above it for a Super Potion.