The effectiveness of a soccer training session is greatly hinged on the coaches intensity, execution, explanation, expectations, communication with the players, and time spend on an activity. However, the most important piece of making an effective soccer training session is to make it competitive and game like by paying attention to the details.

Start with looking at the team as a whole (large group). Break it down a little smaller to see how this affects players as they work in small groups. Now think about each of the individual's roles as they perform their tasks and challenges each individual has, then focus on the mental pressure situations these individual players have. So now that you have drilled down to the focus or topic you should start with the individual player and work your way towards the large group. Here are some ways you can make your soccer training sessions more competitive and game like:

In soccer the shuttle run, often called doggies or yo-yo's, is a fundamental fitness training exercise to build soccer endurance. The shuttle run is a great fitness exercise to include in your soccer training since soccer is a constant stop-and-go sport. This movement represents an important soccer specific movement and is a great exercise to not only build speed, stamina, acceleration, and endurance, but by adding a ball it can also work on controlling the soccer ball at top speeds when your body's become tired and fatigued.
You will need the following to perform this exercise: cones or markers, a soccer ball, and a wall or a person to return the ball to you.

To set up the Dribble/Pass Shuttle Runs exercise mark off 6-8 cones 5 yards apart in a single line. Make sure the player has gone through a proper warm-up and stretch prior to starting this fitness exercise. Each player should perform approximately 4-5 sets.
To begin the exercise, the working player will start with the soccer ball on the first cone and dribble full speed to the first cone, cut the ball quickly and pass to the return player or wall and sprint back to the starting marker without the ball. The return player should stop the ball near the starting line where the working player should quickly gain possession and dribble with speed to the 2nd marker. This pattern should be repeated for each of the cones.
To add a little variation to the shuttle runs exercise, have the return player toss a ball to the working player as they are approaching the starting cone and the working player should quickly control the ball, finish their run to the starting line, and dribble to the next marker as before. A specific body part can be isolated by having the return player throw to a certain body part such as: thigh traps, chest traps, or traps with the feet.
(Source : http://soccerxperts.com/)

Heading in Soccer, Defensive Header, Offensive Header, Essential Skill in Soccer Heading is an essential skill to learn in soccer.
It is crucial for defensive players to clear balls from the back, midfielders to win critical battles in the middle of the field, and attackers to nod a ball past the opposing keeper to score a goal.
This is not as important of a skill for players under 8 years old since the ball rarely lifts off the ground, however, it has proven to be an important skill once the players reach 9 or 10 years old.

Technique for properly heading a ball:

The attacking header techniques are much different than the defensive header techniques. When defending, the purpose of headers is to clear the ball UP and AWAY from an opponent heading the ball from the defensive situation and clear the ball from opponents. Heading a ball high gives other defenders time to reorganize defensively; heading the ball far denies an immediate threat on goal as does heading the ball wide. However, when attacking, the focus is on heading the ball downward towards the goal line to score a goal. We want players to head the ball down towards the goal line because this is the most difficult spot for goalkeepers to defend.

To direct the ball upward players should get their forehead and eyes under the ball and more upward through the ball as soon as contact is made with the ball. Players should use their legs to push the up and through the ball. The emphasis on defensive headers is height, distance and width.

Receiving a ball with your chest is a bit different than trapping a ball with your chest. When a player receives the ball with their chest the player redirects the ball with their chest into space in one touch. Learning to properly receive a ball with your chest will allow players to move into space quicker and avoid high pressure situations.