Currently nuclei that can be studied routinely are 6Li, 7Li, 11B, 13C, 15N, 23Na, 29Si and 31P. While you can tune any core that is your interest to be magnetically active.
For a good spectral quality sample should be as homogeneous as possible and have enough (50-200 mg depend on the kernel). Therefore, it is requested to homogenize the sample in a powder format finely as possible. The sample has to be packed into 4 mm rotors.
See more about solid-state-nmr in our blog.