LIttle thing that helped me improve my Yummi play a bit:

When you attach yourself to an allied champion (not by dashing between them) you trigger the summon Aery shield, and from level 6 on it only has a 5 second cooldown (from 11 its 0).

So in fights, whenever your cooldown is up (no yellow Bar above your W), unattach yourself and reattach to give your ally a shield and to trigger Censer. From Level 11 on you basically have a 2s CD summon Aery shield.

The shield is small, but if you use it all the time it really adds up.