When I'm planning for the season, designing a training session, scouting a team, or watching a game, I always have these 4 phases of play in mind. Along with set pieces, a game is composed of these 4 phases or scenarios. This do not occur in a linear or even cyclical pattern, and the state of the game is constantly in flux between them. Nonetheless, how a team behaves during each of these phases forms the basis for their given style of play.
Think of any world-class team, and their style of play is distinct. It is immediately apparent how a team like Sampaoli's Chile, or Guardiola's Bayern Munich, behaves during each phase of play. Not only is each individual phase of well thought out, but how it fits together with every other phase is obvious as well. Sampaoli's aggressive, attack-minded side pressed like maniacs upon losing the ball to insure they can set up camp in the opposition half; Guardiola's Bayern preferred to connect 15 passes before attacking in order to organize themselves, and push the opponent well into their own third to prevent counter-attacks.
When coaching youth players, it is important to ensure your players understand their individual and collective responsibilities in each phase, but without overwhelming them with information and different scenarios. A single action, or even a single phrase, can be enough to trigger a response. In attacking transitions, the moment we win the ball back, the reaction I want to happen is a quick, easy pass. The phrase I use to communicate this action in training and games is 'control'.
Having clarity in your own approach to these different phases is essential BEFORE you can properly train a team. If you have too many opposing your ideas in your own head for how each phase should be conducted, you will not be able to clearly communicate your ideas to your players, nor conduct exercises that get your ideas across to the team. You also have to consider how each phase will impact the next. I prefer my teams, for example, to employ a patient attack, and circulate the ball looking for good opportunities. If I defend by immediately dropping my whole team to the edge of our penalty area, and allow the other team to build an attack easily, it will be very difficult for my team to win the ball and begin circulation with the opposition entrenched in my half.
When conducting training, I'm sure to include every phase of the game at some point, along with clear instructions for how to behave in each, on an individual and collective level. Having a small set of holistic activities is extremely useful in this respect. In even a basic 10v2 rondo for example, you can work on the movement of the ball with the attackers, or how the players in the middle should defend. In an exercise pitting the back line against the attackers, you can focus on how the attackers should react upon winning the ball, or how the back line should react upon losing it.
Below is a short video on just one phase of play, attacking transitions, and how it can impact and influence the other phases of play.