How do you implement sequence control in PLC programs?

Sequence control implementation methods: (1) Step-based using SFC (Sequential Function Chart) - graphical, clear transitions, supports parallel paths, (2) State machine in ladder - integer step number variable, transitions based on conditions, (3) Shift register method - steps represented by bit positions, shifted on transition. Key elements: entry conditions, step actions, transition conditions, and fault handling. Include step timeouts, manual step advance for maintenance, and proper initialization on startup. Document sequence logic and provide clear HMI indication of current step and required conditions for next step.