The symmetric successive overrelaxation method features the iteration matrix
Either as a stationary method or as a preconditioner, a system in that matrix is solved at every iteration.
The method depends on a parameter $\omega \in (0,2)$. While it converges for every $\omega$ in that parameter range, there is little information in standard textbooks on how to find the optimal parameter in practice. Often, $\omega = 1$ is a choice without further discussion.
What are practical ways of picking a relaxation parameter? Or is picking the parameter a purely theoretical issue?