Monitoring
Monitor system logs for errors and/or deviant behaviour on a daily basis.
Also monitor disk size usage. Disks/partitions running out of disk space will cause system failure.
Ensure time synchronization is set up properly. This is crucial.
Monitor the connectivity to and from the server. Watch for changes in network setup. Typically closed communication paths between server and user stores (LDAP etc.).
Minimize network latency. This is especially important when running in cluster mode.