This paper presents a stationary grouping maintenance strategy for multi-component systems whose structure could be a mixture of the basic structures such as series structures, parallel structures, $k$-out-of $n$, etc. The proposed preventive maintenance decision-making rules are based on the joint consideration of the mean remaining lifetime (MRL), which represents the mean lifetime left before the failure of components, and Birnbaum's importance measure providing the important role of the components in the system structure. For corrective maintenance actions, adaptive corrective decision rules taking into account the criticality of components are introduced. Besides, a cost model considering economic and structural dependences among components are also developed. Moreover, to find the optimal maintenance plan, both analytical calculation and hybrid simulation-analysis method are herein proposed. Finally, the use and the advantages of the proposed grouping strategy are illustrated through a case study of a substation automation system.