You can use focus to remember a target or someone from your team:
Code:
/focus Moderator
Now 'focus' can be used as a unit in other macros. This way you don't have to hard-code "Moderator" into your macros, which makes your system a lot more flexible.

Then you can assist a friendly unit by using the focus:
Code:
/assist focus
or you could assist directly giving a unit name:
Code:
/assist Moderator
And then it's just the usual casting:
Code:
/cast Ban
Because of the assist, you can basically attack whatever enemey that focus(Moderator) is attacking.