I always enter the water first when my students are doing the giant stride so that I can talk them through it. There are two things in particular, beyond what has already been mentioned that I call out to them:
1) "Look at me!" This is so that they don't look down to see where they're going (it's only water). Looking down changes the weight balance and can make the entry awkward and uncomfortable. So just stand up straight and look ahead.
2) "Take a big step with one leg only." Don't jump! Extend your dominant leg and leave the other foot on the boat as long as you can. This prevents hopping, which has the disadvantage of putting very little space between your gear and the edge of the dive platform. Most new divers hop, so most of our boat crews give the divers a little shove to make sure they are far enough away from the boat for safety.