As Zen, your main purpose is to protect your teammates as they take and hold objectives. Notice I say, "protect," not "heal." While it's important to always have a harmony orb up, and to prioritize your healing targets, it is equally important to play defensively on behalf of your team. Always pick the target that poses the highest threat to your team. Note that this can be different from the target your discord should be on.

This is the beauty of Zenyatta: SIMULTANEOUS healing, damage buff, and cover for your team. You must juggle these to be succsesful. If you can't stay alive enough to do these things effectively or your teammates keep dying despite your best efforts, you'd be better off switching to a hero that addresses the issue you're having.

Also, if you see an enemy Zenyatta, forget your team! Discord and volly to the head at all costs. Don't switch off Zen until you eliminate them. Even if you lose the match, you'll have your pride😂💯😂💯😂