Zoom out your camera and move your party list next to your hotbars somewhere in the middle of the screen closer to the action. Moving all of your combat info bars like enemy health bar, focus bar, party list, enemy list, etc. to an area close to the action around your character lets you use your peripheral vision a lot more effectively to manage multiple things.

Clicking on a player to target is not ideal since it's slower and requires keeping an eye on your mouse cursor. I recommend using the function keys to target 99% of the time. Most of the time you'll only need to be using F1-F4 which are in easy reach. If you need to target a dps then the occasional click to target them is okay since most of the time you'll only be AoE healing them and shouldn't need to target them.

I also recommend focus targeting the boss rather than the tank which I've seen some healers do. This will let you see what the boss is casting even if you have a player targeted for healing which can go a long way towards being able to avoid some mechanics. Making it second nature to keep an eye on it will help across all jobs.

Here's my layout with all of my relevant combat stuff just in this small area below my character model (LB bar is just above the pet bar but doesn't show because I'm not in an instance atm):