I haven't read any shooting tactics for gvs when I'm in a tank, however, after MANY sorties I've finally started to identify what they look like at full zoom depending on how close they are to me. My advice would be to head to the training arena and target something small like a fuel tank or a barracks. Get varrying distances away, and then notice how small the target gets from farther away. When you get back to the MA, you will have a better idea of the sizes of targets at farther ranges.
Also remember that HE shells work as good as AP on tanks, especially tigers, but do NOT hit the tank, try and slide the shell underneath the front of it. HE does more damage next to the tank as opposed to actually hitting it. Good Luck man, hope it goes well for you.
--Howitzer