Last month, during the Euro 2008 tournament, there were some great examples of goals scored in transition. From extremes such as balls being cleared off the goal line that resulted in a goal in the far goal 17 seconds later, to teams being dispossessed in their attacking third and being scored on 15 seconds later.
In each case, the goal resulted from a player receiving the ball (either from dispossessing the opponent or receiving an outlet pass from a teammate) and carrying the ball forward while one or more teammates made hard runs off the ball.
While it takes skill and some speed to carry the ball, usually under pressure, as the first attacker, in most of the cases, the goal resulted from the players off the ball willing to make the commitment to make those runs.
In many cases, when a team wins the ball, they relax and take a deep breath, having survived the opponents attack. The teams that are successful in attack are the ones who have the determination to get forward and realize that transition, whether from offense to defense or defense to offense is not the time to relax.
Regardless of age, coaches must instill in players the idea of moving forward (to score) when their team has the ball and the idea of moving back (to defend) when they lose the ball. In Under 6 ball, this is not hard because it is 3v3 and if a coach encourages players to always go for the ball, then they will always be transition in one way or another towards their or the opponents goal. In Under 8 ball, players start to lose their willingness to transition, because at this age coaches start saying stupid things like "You're a Defender! Stay put!" Guess what coaches, when your team doesn't have the ball - YOUR ENTIRE TEAM ARE DEFENDERS!! Also telling a player to stay put is going to result in players that stand and wait for the ball to come to them instead of going to get the ball or being in a place where the ball may come to later.
Transition is about movement, players need to be moving to have transition. If they are not moving, you will not have transition. So not only do players need to be in motion, their coaches must encourage that movement at an early age so they perfect it as they grow.