Elliott Moss found the following elements to be essential to a successful upgrade :
Effective change management and thorough training of all key stakeholders
A business continuity plan to minimize downtime.
Thorough impact analysis, listing all modifications, custom objects and enhancements, and checking SAP notes.
Accurate hardware sizing to ensure maximum return on investment.
Realistic and detailed project plans that depict duration and dependencies of all tasks, technical and functional.
Adaptation and adjustment to the new application version and its functionalities.