To build on what A_Z said, the players pick up little details here and there that they use in future battles: "hey, this guy died really fast when we attacked him with fire" or "my sword didn't work to well the last time we fought one of these". It's more organic and natural.
On the other hand, it can be tough to ignore what you know when you're fighting the same creatures with a different character.
Players can generally figure out the AC by tracking their rolls and whether or not certain values hit. Players should not be told hitpoints, but be descriptive about how hurt they are (I like using "they are hanging on by a single thread when it has 1 or 2 hitpoints left).
You CAN choose to tell the players anything. They aren't owed any numbers, but if it is easier for book keeping then telling them the AC to hit can make things easier and run smoother. Of course, I'd wait until there was a hit against the creature before saying what the AC is; "You strike forth with your sword, sweeping in under the creature's guard, but the weapon skitters off thick scales... it has an AC 19".
You can use description to help with other things. You can describe the monster as slow and lumbering to indicate low reflex save, or strong and hale to indicate high fortitude. You can mention a cunning look to their eye to indicate high intelligence. Sharp claws or blood-stained mouth can give an idea of types of weapons. Of course, also describe armor (or thick hide, matted hair, etc).
|Tamago RPG Superstar 2014 Top 16|
This is completely unofficial, but when describing monster hitpoints, I usually do it something like this:
more than 50% health --> The PCs' attacks are not doing any real damage. They are close calls, or minor hits, but the monster is either able to *just barely* dodge out of the way, or the hit is soaked up by armor/scales/hide/whatever. But it takes something out of them. They might be winded or off-balance, or have bruises or strained muscles, and so forth.
less than 50% health --> The monster is now "bloodied". The PCs have managed to deal some real damage to the monster, and it is injured, but still capable of fighting. It might have a wounded arm, a gash on the leg, or a cracked rib. Successive hits deal more real damage, but the creature continues to be effective in combat.
0 HP or less --> The PCs finally manage to land a crippling blow on the monster, either killing it outright, or damaging it to the point where it can no longer fight.
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D&D 4th edition had a neat system based on a creature being < 50% health. It was a status effect called Bloodied, so you had to tell players when they knocked something down that far. It helped players get a feel for how things were going with any particular monster. Some more math-based players may even try to figure out how many HPs the creature had.
|Tamago RPG Superstar 2014 Top 16|
Tamago, be careful using this method as that sounds a lot like describing Damage Reduction or Hardness. These are qualities a player WILL notice when hitting a creature, so that they can try a different weapon or type of attack.
A fair point, and one that I am actually well aware of. My players have learned to hate the "magic phrase" "It doesn't do as much damage as you think it should. . . " >:-}
Generally, I describe DR as either the weapon plinking uselessly against the monster's hide/scales/whatever (for example, a stone golem), or the monster instantly healing all or part of the damage (e.g. a werewolf). In either case, I do try and make it clear when a hit really did deal HP damage, and I'm just giving a description of the attack, and when the monster actually didn't take damage.