Place proximity mines on the tanks (Vanguard, Heavy Trooper, Shock Trooper) and any other kind of vehicle, except for the assault vehicles such as the AT-TE. A more difficult way is to use a sniper technique. Fire from a safe location. Target the vehicle, wait until the reticule turns red, then fire. Another useful bombardment unit is any that carry a recon droid. Their self-destruct mechanism makes them a formidable bombardment unit.