I keep my projects on target by tracking them methodically.
In this way, I can anticipate any problems before they happen.
Tools that I use are weekly status meetings,
documenting of issues, and earned value.
I use financial measurements to see if each project element is ahead or behind schedule, and if over-expenditure is occurring.
The worse thing that can happen to me as a project manager is be surprised, because surprises can impact the cost, scope, and schedule of the project.
The more I understand the status of the project and its elements, the less chance I have of being taken off guard.