Flatten your stones: If you are using water or whetstones they will need to be flattened (especially if brand new). This is accomplished by setting sandpaper on a lapping plate, adding lubricant and rubbing the stone against it until flat.

Scribble some marks on the stone with a pencil, this will show you high and low spots. This is a critical step, if you are hand planing a board and the plane blade isn’t flat, the board wont be flat, so the stone must be flat! Diamond stones cannot be flattened, but quality ones will be flat from the factory.