Hey man! Join us in holy! Easily Priest is my favorite mage, but everyone has their preference which is why I love the school so much. Each of the holy mages favor certain play styles stronger then other. If you are looking to explore one specifically that will be easier to pin point how to help. In general here is how I think of them
Priestess - Great long game mage, nothing great offensively, but tends to bring out bigger creatures
Priest - Better against short game books then the priestess, He trades the defensive nature of Priestess to have some of the best offensive combos in the game.
Paladin - Really good at aggression. Usually you want at least 2 of level 2-5 creatures to run with him at all times. Generally the faster you want to engage, the more war school you want in this book over holy.
All of them can play any style and still be competitive, but I hope this rundown can help guide you to the ones you want to play.
If you want help in surviving early rushes I highly suggest taking a blind. You can combo it with daze to slim their chance of following through offensively. Holy can shut down solo or buddy builds really easily with the effect rolls and cards like Blind. Another option is just to heal through early aggro. Once their attack spells exahust you can usually cleanup.
Luminous Blast is also a great card to help bring damage on. It's also versatile in that it can be used defensively. Figuring out when you need that daze/stun vs if you want to save it for future damage is something to keep in mind when learning holy. To go with that Dazzle is also from Priestess Academy. This is a great card because Stagger lowers attack spell dice and stacks with itself.
There are a lot more combos in holy, but it really depends on what direction you want to take it. I suggest looking at the cards and starting with the most interesting looking ones for you.
I reiterate and agree with everything Coshade said.
Something of note: while a lot of people like using the forge with the paladin to help deploy his awesome equipment, I actually have just cut forge from most if not all of my paladin books. The reason being is that with a forge, you can most likely get out 1 11-15 mana creature and maybe one 7-9 mana creature in the early game. This is because unless you spend almost all your quick casts and forge actions on super cheap stuff, you will run out of mana to support one of these playstyles. What I like to do instead is get out 2-4 buddies (such as Ehren and Alandell) while manually equiping my mage with equipment and enchantments.