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.
It is probably a rare project that is 100% successful but whatever the final outcome of the project always aim to find some element that was a success and make sure you reflect positively on the successful parts. Hold team reviews to learn from both the successes and the mistakes and take the time to write a report documenting any remaining issues that need to be followed up.