Regularly review estimates, deadlines and milestones to check they are still on schedule. If necessary, update the plan with new estimates and tasks and ensure that remaining tasks are necessary and estimates are still valid. Circumstances can change during a project but question every change and always refer back to the original business requirement as a corss-reference.
All of the tasks listed on the project plan need to be assigned to an individual or team. The person or persons responsible for a task will need to know in detail what the task involves and also the dependencies and timescales, which can be clearly communicated to them using the Gantt Chart.