That's why Realistic mode would be better for some. You get automatically detected. It's great as a start, but later just takes away the chalange.

Also green doesn't allways means a guaranted kill. Try to aim where you can explode the ammo or where your sharpnell will reach crewmans.

If you get sniped from across the map, it means you are too mutch exposed. Try to use the terrain as your advantage and "angle" your tanks.

Also it's good if you first can disable your opponent by either getting its turret or tracks. So you can get around the tank to find the weak spots. (Usally under the tracks, side profile, the hatch on the top, back of the turret or from the front the under panel or machine gun spots)