Route 3 is a semi-long route that connects Pewter City in the west with Mt. Moon in the northeast. You will run into many trainers along the way, most at the start of the route. It’s best to return to Pewter City and heal your Pokemon at the Pokemon Center instead of using items since you’re so close to town. The first three trainers are in a row:
Now that the route is clear, you can quickly go to the Pokemon Center at the foot of Mt. Moon to heal your Pokemon. Speak to the man in black to buy a Lv. 5 Magikarp for 500 money. Some say this is a dumb choice since you can easily catch Magikarp later on, but that won’t be until you’re about to get your third badge. If you get one now and train it along the way, it will evolve into the vicious Gyarados by level 20. Send it out each time a trainer sends out their Pokemon, then quickly switch to another Pokemon. The Magikarp will earn half of the exp from the battle without doing anything.
You can catch some more Pokemon on Route 3 before going onward, just make sure you have enough supplies to get through Mt. Moon.