Hearthpwn

Personally, I'm not the author of that deck, I've just made this for one overview of ladder. But as far as I understand, you should prioritize Manawyrm and Archanologist on mulligan. It is also OK to keep Babbling book, KT Mage+secret and Frostbolt, especially if you have something aforementioned. Also if you have no turn 1-2 play, you could keep Valet to ensure you not get rushed versus agro. Versus slow opponents (like priests or warlocks) AI and Primordial glyph could be good as well. Crystal Runner is good to keep against a slow deck if you have a secret. If you have Archanologist, don't keep secrets, you'll draw it and better to have some early game instead.

Then you just want to build a strong board, make good trades and mess enemie's game plan with secrets. Like playing Counterspell against Paladin on turn 5 to try and catch Steed (most often you won't but still worth trying). Antonidas is good in combination with Primordial Glyph and Burgly Bully. These two cards provide you coins and cheap spells to play with Antonidas, so you get more fireballs. And it's often much neeed burst against slow decks. It's also some kind of skill to determine when you should forget about board control and go all-in face rush with minions and fieballs/portals.
Against agro you mostly want to kill all their minions and face only when you're safe.
I'm sorry in case of some mistakes, but I hope my comment would be helpful. GL:)