One thing you can do to keep your system in shape is to IPL it regularly. You don't need to IPL it every day or even every week, but make a point to reserve some time to IPL at least twice a year. An IPL each month may be the optimum frequency.
During an IPL, the system performs a number of "housekeeping" chores it cannot do at any other time. It rebuilds the access paths to keyed files and reclaims space that was previously used by spooled files. IPLing also makes certain changes (such as a change to system value QSECURITY) effective.