The second major class of targets that I always consider is enemy heavy tanks. In my mind, this includes any vehicle with AV12 or higher with significantly threatening weaponry.
There are two things you need to consider when dealing with enemy tanks. The simplest and most straightforward is destroying them. Though lascannons and missile launchers have the capacity to take out heavy tanks at range, they cannot do so reliably. In general, this will require your units to get close and engage the tanks with melta weapons or in assault. While this is your ultimate objective, it often is not feasible until late game.
While you’re waiting for your chance to destroy enemy tanks, you need to minimize the damage they do to your army. For Blood Angels, this often means using speed to stay out of their lines of fire. However, it is important to be able to suppress enemy tanks to grant your troops freedom to move through their field of fire. This is generally done with large amount of medium strength firepower, such as that provided by autocannons. Your goal here is to inflict any damage result which will prevent the tank from firing. Once you stun or shake a tank, switch your firepower to targeting the next one. Suppressing fire is only concerned with preventing the maximum number of tanks from firing in the next turn.
When prioritizing targets, always be sure to think about the damage each tank will be able to do in the next shooting phase, not just its overall potential to deal damage. In other words, target priority must take into account not only what guns the tank has but what it can shoot at. No matter how dangerous a tank is, it’s low priority if it doesn’t have any target to shoot at.