Start reviewing your Transport Management System. Are there transports that have not made it to Production, should they be deleted? Review incomplete developments, should they be shelved? Review Add-ons that are no longer supported, what’s the plan going forward? Our experience here is that organisations leave this as they fear breaking anything. Attacking this cleanup ahead of schedule will be less painful than doing it during the S/4HANA jouney. You may want to consider implementing a toolset to manage SAP projects. Tools such as SAP’s Charm, Revelation Software’s Rev-Trac or BASIS Technologies’ Active control may assist with the management of developments in an SAP landscape during BAU cycles as well as projects. They add a level of governance that is hard to achieve using manual processes.