  Near-term quantum devices are subject to errors and decoherence error is one
of the non-negligible sources. Dynamical decoupling (DD) is a well-known
technique to protect idle qubits from decoherence error. However, the optimal
approach to inserting DD sequences still remains unclear. In this paper, we
identify different conditions that lead to idle qubits and evaluate strategies
for DD insertion under these specific conditions. Specifically, we divide the
idle qubit into crosstalk-idle or idle-idle qubit depending on its coupling
with other qubits and report the DD insertion strategies for the two types of
idle qubits. We also perform Ramsey experiment to understand the reasons behind
the strategy choice. Finally, we provide design guidelines for DD insertion for
small circuits and insights for large-scale circuit design.
