Communication is Key
There are many distractions that are apart of running a business. The supplier has no record of your order, even though you do, and you need the materials right now. A client remembers having told the sales person something, but the sales person doesn't remember it. All of these examples are issues we deal with on a regular basis and are always trying to eliminate.
A successful job depends on the transfer of information between the appropriate people at the right time. specifically when you're working with clients, it is imperative to stay on the same page. How do you make this occur more often than not?
Document every conversation.
You need to tell the client (Builder, supplier or anyone else) something. You call them. Maybe you even connect with them instead of leaving a message. Regardless, write them an email recapping the call, what the issue is and how/when it can be resolved. Why? It helps to avoid mutual mystification, which is when two parties converse, and walk away with a different idea of what was agreed to.
Always set a date by which you will be talking or meeting with to discuss the project.
If the general contractor and the client (or who ever the two parties may be) each work to communicate and keep track of everything, the task at hand will be much simpler and more time efficient.