Guns always get a first shot, so if you're expecting an enemy gun, here's couple advice. Move your tanks together where you believe the gun is located. Once the gun start to shoot your tanks the rest of your tanks hopefully destroy it, or you can move something light/inexpensive first and hope your enemy reveal his guns, and you can take them out with mortals.
Sounds pretty good to me, especially if you're holding the flag, hide, and wait for your enemy and ambush them. Don't shoot over 150 meter it's wasting a bullets, unless you want to delay your enemy and keep them pinned little bit.
You take always heavy losses when moving on open ground. One way to cross open is to use "move to contact" and "hide" command, so when your inf spot an enemy they hide, from there you can keep sneaking or advance/run to nearest cover, or make smoke.