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In this paper, a decode-and-forward (DF) single relay model in a Rayleigh fading environment is considered. The outage probability and ergodic rate for this model are derived. With the objective of either minimizing the outage probability or maximizing the ergodic rate, optimal and approximately optimal transmission strategies are developed through selecting appropriate transmit signaling and/or spatial power allocation. The derived transmission strategies only require the knowledge of the second-order statistics of the channels at the transmitters, which can be readily acquired in practice. Simulation results demonstrate that the optimal transmit signaling and/or spatial power allocation can offer considerable performance improvements over the equal power allocation strategy.