A standard team composition in AoS usually involves two AD carries, two tanky-supports, and one AP caster carry. One of the most ideal compositions looks something like this:
The strength of this composition lies in the fact that in AoS, one hero is usually taken out of fight completely. This means that a team needs to have at least two AD carries to win a teamfight. Only one burst AP caster carry is required due to the fact that his or her job is mainly to kill off the opposing squishy AD carry. Finally, the two supports are there to ensure that teamfights go favorably.