One of the first things I like to tell new healers is to go into a dungeon and over the course of that dungeon look closely and get a feel for how much each of your healing skills does on a tank and learn to connect that amount healed with when you should casting the spell

For example if cure 2 heals the tank for 70% of their health bar in general there is really no reason to start casting cure 2 till the tank hits 40% health, there is flexibility here based on how quickly the tank is dropping but in general it’s a good rule of thumb that is especially useful if you pick up a shield healer that has permanent passive regen

But yeah at your level in general you want to open with regen, only cast cure 2 when the tank is about 10% above how much you know cure 2 heals for and use lucid dreaming on cool-down (don’t hold it), as you get more skills you’ll come to realise how much each one heals and how much each slow the tanks HP dropping and can mix and match sets of those skills as you become more familiar with them