I go similar to Sam.

A:
/Targetenemyplayer
/cast Hex

B:
/Targetenemyplayer
/Targetenemyplayer
/cast Hex

C:
/Targetenemyplayer
/Targetenemyplayer
/Targetenemyplayer
/cast Hex

D:
/Targetenemyplayer
/Targetenemyplayer
/Targetenemyplayer
/Targetenemyplayer
/Cast Hex

Etc.

/Targetenemy - this will target a hostile target, the same as pressing Tab.
/Targetenemyplayer - this is similar to the above, except you cannot get pets, totems etc, only players.
Adding the 1 to the end reverses the order, so it is like Tabbing through until you get the last possible target without resetting to one of the first ones.

These depend on facing, Tab won't cycle through enemies behind you.