Add this to what has been said already:
It also helps to zoom the clipboard map (only the map part, not the whole clipboard) so you can really get in and select your point with accuracy on the field. It helps to know where the majority of targets on that field type exist also (like on the large field there is a relative tight grouping of hangers in some locations like the north side of the field).
Then fire away, making slight adjustments until you hit something and then move around the field between each salvo to spread around the damage. If you feel you are off-target, then re-select a location on the map, and start again.
Remember, there is quite a spread possible between salvos, so one may hit, and the next may miss, both aimed at the exact same point. I usually give 2 salvos in the same spot to see if there is anything to hit.
-Soda
The Assassins.