Best Practices for Estimating Large-Scale Construction Projects

I'm a building cost estimator who has experience with large-scale projects for several years, and I would like to present some of the best practices in this forum. 

At the beginning of my career, I was not realistic in the process of estimating of the cost hence I had unexpected materializations and budget troubles. Have your projects gone off the rails due to inaccurate estimates at some point or other?

The most important step that I took to increase my estimates that I use Construction Estimating Services. These services allowed me to find new ways of planning through detailed information given about how much the materials and labor were and what time that took. This of course meant I had been more careful when doing work. Who plans for big-size projects? What are your methods? Do you normally hire specialized people with traditional methods? I’m looking forward to listening to your take on how you make estimates faster and still maintain their accuracy.