first off, /assist assumes you do not have macros to help your target or your focus. if your macros have target=targettarget, or target=focustarget, having /assist is pointless.

second, make your main the focus.


third, use this to follow:

/target party1
/follow


fourth, use this to attack what your focus/main is targeting.
/cast [target=focustarget, harm, nodead] [] Smite


end.