In multiple-input multiple-output (MIMO) transmission, precoding has been considered a promising method to improve the system performance. In general, the precoder design criterion depends on the detector used at the receiver. For the maximum-likelihood (ML) detector, the optimum precoder design criterion is equivalent to maximizing the minimum distance of received signal constellations. Several precoding methods have been developed in the literature. However, most of them use numerical searches to derive the precoders and require table look-ups in realtime applications. In this paper, we propose a simple but effective method to solve the problem. The proposed precoder has a simple closed-form expression and no tables are required to store. Simulation results show that the proposed precoder can provide almost the same performance as existing precoders.