Spatial permutation modulation (SPM) has been proposed and demonstrated as an efficiency multiple-input multiple-output (MIMO) technique which generalizes spatial modulation (SM) by exploiting the time coordinate for further transmit diversity gain. In particular, SPM activates the transmit antennas at successive time instants by the permutation vector which brings the information bits. In this work, we elaborate on the design of the permutation set of SPM and the mapping between the permutation vector and the information bits. A MIMO system with 6 transmit antennas and 16 permutation vectors in the adopted set is applied as an example for these two design issues. Numerical results demonstrate that, by using our mapping rules and designed permutation sets, the error rate of the SPM system is greatly improved.