Set the dice so that on the top of each die the 3 is facing up in a V shape. This is traditionally the "set" for the dice, so all players know you're not cheating or doing something unfair to the game. Usually, there's a designated surface the dice have to hit. In casino craps, the dice must go all the way to the back wall of the table for it to count. This is why most street craps games are played against walls. Generally, you'll be a few feet away and roll against the wall, or some other kind of backdrop.

Summary:
When you're the shooter, roll the dice correctly.