Moira’s healing orb provides an excellent boost to your healing output and can save teammates from a lot of situations.
You should aim to bounce it around as many damaged teammates as possible to get maximum value.
Genji can deflect your healing orb and use it to heal him and his team. Make sure you don’t throw it directly at him when duelling him.
In some situations you can bounce an orb on a low roof to gain easy access to healing, which makes you a lot tougher during 1v1s.
Higher level D.Va players will try to predict when you throw your orbs so they can immediately destroy it with defence matrix. Wait until she is distracted by something else or try to fool her with false orb throws.