From Bulbapedia, the community-driven Pokémon encyclopedia.
This is part 1 of a Walkthrough that covers the journey through the Hoenn Region in Emerald.
After reading and completing the start-up screen with Professor Birch, you start in a moving truck. After exiting, you will meet with your mom who tells you to set your clock, once you've done that mini-quest, head back downstairs. The mom will be watching TV when the player goes back downstairs.
She quickly calls you to watch the T.V, saying that your dad might be on TV. However, the program ends. Your mom will continue to talk, and you learn that your father is the gym leader of the Petalburg City Gym. Your mom then suggests that you go and meet May (if you chose being a boy) or Brenden (if you chose being a girl), who lives right next door, they later become your rival. May/Brenden talks a little about what they want to do as a Trainer, and that Professor Birch is their father. They'll then leave.
You then must go rescue Professor Birch on Route 101, north of Littleroot Town, from a Zigzagoon. You will choose a Pokémon from his case to battle the Zigzagoon, either Treecko, a Template:Type2, Torchic, a Template:Type2, or Mudkip, a Template:Type2. This Pokémon will become your Starter, so choose carefully. After the Zigzagoon is defeated, Birch invites you to his lab. He talks a little bit about the responsibility of being a Trainer, then lets you keep your Pokémon. He suggests that you go to Route 103 to battle May/Brendon (and won't stop talking until you say it's a good idea).
In order to get to Route 103, need to take Route 101 to Oldale Town. With ledges blocking the way, you must go through the tall grass to keep moving north. Pokémon can be battled, but not captured, seeing as you don't have any Poké Balls yet. It's good for the sake up the upcoming battle that your Pokémon gains EXP, so it would be wise to knock them out.
Once in Oldale Town, you can learn about Poké Marts from the man in an apron walking outside. After telling you about them, he gives you a Potion as a "promotional item." Apart from the Poké Mart, there's a Pokémon Center and a few people who will tell you about certain basic foundations for Trainers. There's also a man blocking Route 102. Seeing as your rival is as powerful as you are, it would be a good idea to heal your Pokémon at the Pokémon Center.
Travel northward up Route 103. There are a few Trainers and some tall grass. At the end (a dead end) is your rival. Talk to May/Brendon, and you'll battle. Your rival has one Pokémon: a Level 5 Torchic (if you picked Treecko), Mudkip (if you picked Torchic), or Treecko (if you picked Mudkip). After you win, (s)he'll leave, and tell you to come back to the lab. You'll have to walk back to Littleroot Town, but this time you can avoid the tall grass by jumping over the ledges.
Once you get back to Prof. Birch's lab, he'll give you the Pokédex, and your rival will give you five Poké Balls. You can then leave for Petalburg City. Before you go, your mom walks out of your house and gives you the Running Shoes. She reads the instructions (hold down "B" while you're walking) and lets you go on.
On Route 101, you can battle:
Poochyena (common - 45%)
Wurmple (common - 45%)
Zigzagoon (rare - 10%)
On Route 103, you can battle:
Poochyena (common - 60%)
Zigzagoon (common - 30%)
Wingull (rare - 10%)
When you go back to Oldale Town, the man blocking Route 102 will be gone, allowing you to get to Petalburg City.
Once in Petalburg City, you can walk into the gym and talk to your Dad. He'll tell you a little about battling Gym Leaders, and that he won't battle you yet because you're too weak. You will be able to battle him when you have four badges. He'll then tell you that you should head for Rustboro City to the north-west and battle the Leader there. You'll have head west (right) of Petalburg Ciy and onto Route 104.
On Route 102, you can battle:
Poochyena (common - 30%)
Wurmple (common - 30%)
Lotad (uncommon - 20%)
Zigzagoon (uncommon - 15%)
Ralts (rare - 4%)
Seedot (rare - 1%)
Once you get out of Petalburg City, you'll come to Route 104, a small route that leads to Route 105 and the Petalburg Woods. Here you will also pass by an empty house; it will become important later, but for now it's empty. Continue on to the Petalburg Woods to the north. Once you get there, aim northward and you should get out easily. There are a few Trainers to battle, and one important piece of storyline.
When almost out of the woods, you will see a man getting attacked by an Aqua grunt. You will have to rescue him. The grunt only has a Poochyena, so unless you're Pokémon are weak from the trip through, he should be beaten easily. Once you do, he'll run away, and the man will thank you gratefully and reward you with a Great Ball.
The rest of the trip is simple. After you get out of the Petalburg Woods, you'll find yourself in the northern part of Route 104. There are some more Trainers, and then you can enter Rustboro City.
On Route 104, you can battle:
Poochyena (common - 40%)
Wurmple (uncommon - 20%)
Marill (uncommon - 20%)
Taillow (rare - 10%)
Wingull (rare - 10%)
In the Petalburg Woods, you can battle:
Poochyena (common - 30%)
Wurmple (common - 25%)
Shroomish (uncommon - 15%)
Silcoon (rare - 10%)
Cascoon (rare - 10%)
Taillow (rare - 5%)
Slakoth (rare - 5%)
In Rustboro City, you can battle Roxanne, a Template:Type2 Trainer. She will hand out the Stone Badge to Trainers who defeat her, she will also give you the TM Rock Tomb. Having the Stone Badge allows you to use the HM move Cut outside of battle. Cut is not required to move on, but it helps. The HM (HM01) is given out by The Cutter, whose house is in Rustboro City.
There are two Trainers in the Gym before you face Roxanne, but you don't need to battle either of them. It's your choice.
In Rustboro City, you can find:
Seedot (Only One - Trade Ralts)