The most important aspect of your pool is the design. Take your time understanding every aspect of your design prior to signing any agreements, and especially prior to starting construction. The following are the most important things to understand:
Pool location and shape - Make sure you see and approve a "scaled" drawing with all measurements and depths on it.
Equipment location and type - Approve the actual site and footprint of the pool equipment.
Material list - Understand the materials you are getting or at minimum, the budgets included for the materials.
Plumbing sizes - Make sure the plumbing is not undersized for the equipment that you are using. Pipes that are too small can shorten the life of your equipment and create high energy bills.
Inclusions List - You should have a list of everything included. This list might include things like permits, engineering, main gas and electrical lines, inspections, etc)
Understanding these things will help you to get a more accurate and competitive estimate, assure an easier construction experience, and make you a more educated homeowner.