Instructions
Fly to Pastoria City and enter the Pastoria Great Marsh through the building at the northernmost part of the city. Pay 500 Pokedollars to enter the Great Marsh and play the Safari game. You will receive 30 Safari Balls that you can use to catch Pokemon.
Walk through the tall grass, fish or surf on water in various areas of the Great Marsh to encounter wild Pokemon. Once you encounter a wild Pokemon, you will be given options to throw a Safari Ball, throw mud, throw bait or run away.
Select "Throw a Safari Ball" to try to catch the Pokemon. If you are unsuccessful, you may choose to throw mud or bait at the Pokemon. Throwing mud raises the Pokemon's catch rate, but makes it more likely to flee. Throwing bait at the Pokemon lowers its chances of fleeing but subsequently lowers its catch rate. If the Pokemon flees, continue walking around the tall grass to encounter another wild Pokemon and repeat this step.