Just as an addendum to my comment regarding fishing for lilies - this is an non-optimal strategy because, in an ideal world, a WHM casts Cure / Cure II very infrequently. Unfortunately, we're all not savage-tier raiders so understanding some of the other (albeit weaker) parts of your kit can also help you get through scenarios that feel insurmountable.
Also, as others have said, you're a priority as if you, as a healer die, everyone will die with you afterwards.
The one advice I always like to give healers is understanding the fights. A lot of bosses work in predictable time frames so if you can pre-position yourself to minimize movement and maximize uptime, it'll allow you to heal / DPS more frequently. This comes with time and experience though, so don't get discouraged.
