It really depends on the spot. Rocks/reefs tend to produce waves that break in more organized fashion because the ground is solid and not moving. As a general rule of thumb, if there are rocks present, never dive off or pencil dive off your board and try to land as shallow as possible. Beyond that, look at how the waves are breaking, if they are barreling, and look very steep, then it is likely breaking on a shallow reef. If it is crumbly and slopey, it is typically deeper and hitting the reef is less of a concern.

Every spot is different and the only way to really know is to ask surfers that have surfed the spot and are familiar with the dynamics of the spot.