WELCOME ABOARD!
Sharkbit's initial post reflects perfectly what the real guys had to go through to set up a proper attack. At least we have the luxury of being able to mess it up and try again (and even die and try again). Use the external views until you understand what's going where, take your time and it'll come to you.
I usually try to get in front of the convoy and lie low until I can fire from 500 metres or less. That way my bad shooting doesn't bite me as often.