Ok, check-in time. You should be in Vermillion City with three badges and at least 25 Pokémon. If you're doing really well, you could have up to 30 Pokémon. Whichever Pokémon you chose for your starting monster should be in its second stage. Now, gather a team of Water and Flying Pokémon and enter Diglett's Cave.

If you have a Bicycle, use that while going through the cave. There's nothing spectacular in there, just (what seems like) miles and miles of mole-like Digletts attacking you.

When you exit the cave, you'll be on Route 2. Head south, making sure to check all the houses. In one, Professor Oak's Aide will give you the Flash HM, and in another, a trainer waits to trade with you. If you have an extra Abra, you can trade it for a Mr. Mime.

There are also two items a little bit south of the second house: an HP Up and a Moon Stone. This should be your third Moon Stone; if you haven't gotten the other two yet, it's ok because you're headed for Mt. Moon again!

Make your way back onto the main part of Route 2, and head toward Viridian City. In the lower left part of the town, a fat kid will give you TM 42, Dream Eater. Teach it to your Drowzee; he's the only Pokémon who can accept that TM except for the ghost family, and they learn it on their own. Now, head back up toward Pewter City.

In Pewter, go up to the back side of the museum and Cut down the bush. A scientist inside will give you the Old Amber, which you'll need later in the game.

Time to revisit Mt. Moon. If you still need to capture any of the Pokémon that live there, make sure you bring a lower-level one that won't kill your enemy with one hit. Or, if you already have a Zubat, Geodude, Paras, and Clefairy, just use a Repel.

You've made it through Mt. Moon a second time. Great! Now, go into Cerulean City, heal your Pokémon, and continue east. Go through the same building you did the first time (the one where the people got robbed) and this time, instead of going south, go farther east and Cut down the bush. There are zillions (literally!) of trainers on the way to the Rock Tunnel, so watch it!

After the grueling struggle to get to Rock Tunnel, you're rewarded with a visit to the PokéCenter. What? That's all? ^_^ You can also see the Power Plant from here, but you won't be able to get to it yet. So, enter Rock Tunnel (be sure to get the hidden item on your way in; it's behind one of those rock thingys), use Flash so you can see where you're going, and continue onward.

After you've made it out of the Rock Tunnel, you'll be very close to Lavender Town. Still, there are a few trainers that will challenge you on your way there. If you want to avoid as many battles as possible, take the right route. The left path has three trainers, the right path has only one.

Ok, now you're in Lavender Town. There's nothing you can do here until you get the Silph Scope from Giovanni. If you'd like to build up some of your Grass or Electric Pokémon, head south and challenge the fishermen. When you get sick of that, travel west. In the field that's completely blocked off (the only way to get to it is to use Cut) you can find a Vulpix or a Growlithe, depending on which version you have. Vulpix is found in the Blue version, and Growlithe is found in the Red version.

Now, continute westward to Celadon City!