The first step in surveying a dental cast is to check the anterior-posterior tilt. This step is crucial because it helps establish the correct orientation of the cast so that all subsequent analysis is accurate. Tilting the cast anteriorly or posteriorly allows the surveyor to identify the most favorable path of insertion and determines the locations of undercuts that will affect the design of removable partial dentures. Incorrect tilt can lead to improperly located survey lines and misinterpretation of undercuts. Therefore, positioning the cast correctly ensures precise marking of survey lines and analyzing rod placement.

Reference: McCracken's Removable Partial Prosthodontics, Jacob S. Segal, 13th Edition.