I run a pretty tight ship, and 90 times out of 100, my gunner is on his gun, ready to shoot the target me or my engies spot. The only exclusion to this is when its been a long time without a first spot. Then we all start scratching our heads until we eye something.
Also, if you get spotted, that means they can see you, so you should see them. After that initial spotting game, it really just becomes a matter of memory and maintaining those spots. Re-spawns are easier, since you can kind of guess where they are coming from.