Study what you like. I would suggest taking a nice broad range of classes, but I’d give that advice anyway, regardless of grad school intent…
If I wanted to prepare myself for law school, I’d major in maybe Political Science, Sociology, Philosophy, Psychology or Econ (and take classes in the rest)… and take a nice range of other courses from areas like Math/Science, English/Lit, Communications & Linguistics, Business/Marketing/Finance, History/Anthro, etc.