[C] Prowler is most commonly used to reveal or pressure players in areas of the map that your team wants to gather information in, or show presence in.
[C] Seize is very incredibly effective when combo'd with your teammate's utility. You could, for example, trap enemy players in a position that opens up the possibility for a Raze on your team to follow up with [E] Paint Shells and finish them off.
[C] Haunt has an incredibly high skill ceiling. This gives you the opportunity to get creative with how you use it. But, it's often best to use simple, but difficult to react to Haunts that create opportunities for your team to take advantage of.
[C] Nightfall sends out a massive wave that deafens, decays, and trails enemy players caught in it's path. This, especially when combo'd with some of your other utility, can create the opportunity your team needs to secure a round.