Many good advices here, but adding one I feel is missing. Try to never yell out for heals. It doesn't help. The healers are aware of your health. Quite possibly they are more aware of it than you yourself.
Also, if you really really would like to learn start a alt that you can heal with and heal some instances. The first time you heal a instance you will see all the tank's mistakes and be irritated on that. The second time it's pretty much the same. But maybe the third time you will learn what you could have done to cover for others mistakes. And that's the first step on learning what healers can do and can't do - experience it.
"We have two ears and one mouth for a reason." - Buddhist belief.