Start with the rear brake

When you want to brake with the shortest possible braking distance, you start by using the rear brake. Of course, you don't slam it. In fact, you only use the rear brake to start a process of shifting weight from the rear to the front wheel. This will cause the springs to get contracted, which will decrease the chance of a lifting rear wheel, and which will stabilize the bike.

A little bit later the front

By using the rear brake first, there is already more weight on the front wheel when you use the front brake. Because of that, you can squeeze the front brake harder than when you would have started braking with the front brake.

Lay on and squeeze through

But even then, it is not advisable to squeeze the front brake as hard as you can, at least not in the beginning. You should start gently and then squeeze on when the weight has shifted to the front, because the grip of the front wheel will then be at its best.

To imagine what "squeeze on" means, imagine squeezing half a lemon.