Given an ample, Hausdorff groupoid G, and a unital commutative ring R, we consider the Steinberg algebra A R (G). First we prove a uniqueness theorem for this algebra and then, when G is graded by a cocycle, we study graded ideals in A R (G). Applications are given for two classes of ample groupoids, namely those coming from actions of groups on graphs, and also to groupoids defined in terms of Boolean dynamical systems.