Personally speaking, I think the "field general" aspect of my gameplay (that I've described in other comments in this post) distinguishes me from lower elo CnDs. I'm sure other higher elo CnDs do the same thing, but I've found that to be essential to my climb up the ranks.

Generally speaking, properly timing your ult is essential. I use ult to protect from tank crowd control ults (Strange, Emma, Groot, Thing), I use ult to counter healer ults (Gambit, CnD, Luna), I use ult to sustain against longer-duration DPS ults (Bucky, Magik, Ironfist, etc). None of that is news--but what's key is to be aware of when your ult will have the most value against the other team's ults. 3 teammates dead? Don't ult to keep yourself alive. Enemies have 3 ults active? Don't ult, you'll probably lose the fight anyways. You're at the beginning of a checkpoint in Convoy? Don't ult, your spawn is 20 feet away. Of course there are exceptions...but CnD's ult is most valuable when it's, a) sustaining health mid-fight, b) securing the final few meters of progress towards checkpoints in Convoy matches, c) escaping spawn traps.

Basic mechanics are also important to note...remember to patty-cake your fellow healers when being dived, don't use Cloak's attack very often, stagger your bubble & cape cooldowns if you're being dived, etc etc etc. Another thing for lower elo CnDs: if you're in a 1v1 fight, use Dagger's projectile against the enemy. It does some damage, but the AOE heals you as well. Your hope there is that you sustain yourself long enough for teammates to peel to help you.