I find that target priority begins when the opposing team picks up their offensive/defensive supplies. Don't get stuck thinking a certain role is going to be the first priority for each single game. Recognize the icons for defensive supplies, safeguard, and tank LB and learn to hold on to your cds/retreat/switch targets when you notice them. More importantly, learn the importance of medals. There is another new thread with a link about medals and how they affect you and prioritization.