Use the players on the team in their specific positions at all times, you could have two sets of 3 and 3 as attackers so they learn to switch on to defend also; like defending from the front. A 3 v 3 + 1 attacking and defending game
Emphasize the diamond set up as in the attacking phase of the 4-2-3-1 is between the opponents back players and their midfield to gain an overload advantage.
Good for teaching strikers how to switch on immediately from attacking to defending so have 6 attacking players in there unless you want to work on defending so have the relevant defenders in place.
Build up can be slower using the outside players until the right moment appears then it has to be as fast as possible with quick combinations plays by the attacking team.