The goal kick is the most dangerous set play for lower level teams. The attacking teams score more goals from the defending team's goal kicks than any other opportunity until a team learns how to successfully clear the ball from it's defensive end.
The biggest problem is set up. All too often, the defending team moves too far away from the goalie. Anyone who watches pro soccer sees the players all move to mid field and the goalie kick it over their heads. Alas, most keepers don't develop the leg strength or skill to kick the ball that far until they reach high school. Hence, the keeper ends up kicking it at his teammates (and the opponents) who are all facing the goal. It's only natural that the ball is played back towards the goal on the first touch and the other team is off to the races.
To prevent that scenario, here's a few basics to minimize the other teams chance of scoring after your goal kick:
Here's a quick listing of the rules pertaining to goal kicks (FIFA Soccer Law #16) :