Establish estimates of what it will take to see a project through from start to finish. These estimates include such things as the size and scope of the end product, the number of resources required, special skill sets needed, types of computing resources required, and so on. These estimates can be derived from formal models, from similar projects from the past, or from consensus of experienced opinion. However you approach it, the idea is to estimate intelligently using as much data as is available to you.