Learn from past projects
For all work packages, learn how the work evolves over time, and at what points estimations where not in line with reality. Analyze this way what can be learned from projects.
Export to Excel for even more detailed data.

Monitor your top level milestones prediction. If you see milestones slipping away (upwards in the chart), look for actions to bring them back in track. Scale down the project or do things in parallel and keep your project timing under control.