To increase maturity in SDLC is is generally recommended to implement the Primary SDLC processes. If you already have these processes fully optimised and have reached Maturity Level 5, it is time to implement the Supporting and Organisational processes. See Maturing your SDLC for more details.
The Organisational Life Cycle Processes include four process groups, they are Management, Process Improvement, Resource and Infrastructure and Reuse.
Management Sub Processes
The Management Process Group includes Organisational Alignment, Organisational Management, Project Management, Quality Management, Risk Management and Measurement.
Process Improvement Sub Processes
The Process Improvement Group includes Process Establishment, Process Assessment and PRocess Improvement.
The Resource and Infrastructure Sub Processes
The Resource and Infrastructure Group includes Human resource management, Training, Knowledge management and Infrastructure.
The Reuse Sub Processes
The Reuse Group includes Asset Management, Reuse program management and Domain engineering.