Find a good vantage point (bit of elevation helps)
Take out any acks or manned guns with HE rounds.
Roll into town, blast buildings at point blank range.
Other than that trial and error, not too much zoom, use mouse to show where your last hit was.
You can smack buildings without too much trouble from 1-2k out. Farther is harder
I have not used them that much, but they sure seem to work slick for taking port, vh or town down.
If you had someone drop supply's thats even sweeter.
