Planning ahead and communicating with the supplier are fundamental aspects of ordering ready mix. Though every contractor has preferences on how to do things, here are some important considerations.
What kind of concrete are you ordering? Many specifications require submitting mix proportions for concrete proposed for the job. Talk to the ready mix supplier early to see if a proven mix can meet the specified requirements. In many contract documents there is a strength penalty for new mixes, since there is more uncertainty about them than mixes with a proven record. Where there is no information about the mix, it's necessary to increase the strength margin.
The producer needs a variety of information before delivery. Clearly indicate how much concrete will be needed, where the trucks should arrive at the job, and when the pour should start. Identify who will be in charge at the site, and who is authorized to reject a load. The needed delivery capacity is best stated in cubic yards per hour, rather than trucks per hour.