Instructions
Travel to Lilycove City, which is to the west on Route 124 and to the east on Route 121.
Enter the Pokemon Contest Hall, which is slightly south of the center of the town.
Walk to the right of the counter. You'll see four blocks. These are the berry blenders. One of them doesn't have anybody using it, while the others have anywhere from one to three users. To get the best Pokeblocks, use the one with three users.
Select the berry you want to add to the mix. Once you've inserted the berry, the blender will start to spin. Your goal is to make the blender spin as quickly as possible. You do this by pressing the "A" button when the blender blade points to you. When it's done, you receive a Pokeblock.