Play even sided matches, small sided to full 11 v. 11.
Depending on the fitness expectations of the coach, the team is asked to play a particular style. For example, if the coach wants them to increase the fitness demands on the players, they could be asked to play man-to-man defense and play high pressure. If pulse rates need to be lower, the teams could be asked to play zones and low pressure.
Field size can also effect the fitness demands. By asking teams to play high pressure on a large field, with numbers down, the fitness demands would be high.
Make sure extra balls are available so that play can proceed uninterupted.