About Mattj's method with the shaking ground or grass to confirm your seed. . . where a shaking patch will appear is also based on your walking pattern. I hit my seed around 7 times for my Kyurem, walked different paths each time, and the shaking patch appeared in different locations. One of the times it appeared directly under me. :(
However, the last two times it did appear in the same spot. So I would recommend walking the entire length of the map one way and back until the shaking patch appears.
However, the last two times it did appear in the same spot. So I would recommend walking the entire length of the map one way and back until the shaking patch appears.