Well.. for Zarya. Bubble ur teammate/yourself after they get damaged abit first.
For Ana, sleep dart tanks, always when you have opportunity. But save it when you expect one of the dps to be using ulti soon.
Use nade offensively whenever possible. Save if there is an opponent consistantly targeting you. Combo with a shot, nade, shot, sleep dart, run.
To kill a sleeping target, wait till the end of their sleep and do a nade/punch/shot combo.