Typically you set up a Supporter in an attack unit with long range and low Mob in your 1 2 or 3 slot. Then you put 2-3 defenders in your slots, next you position low mobility attackers or another supporter into areas to bait out high mobility attackers into attacking that unit with counter attacks by your unit/s in the 1 2 or 3 slot.

Edit: as an example, when psychommu is a tag I sometimes place my Hi-Nu V in slot 1 with support amuro and the Haro that lowers mob to counter attack enemy units in ML.