This is just a hypothetical, but how much should a DM use player tactics with (intelligent) NPCs?
Take the Help action; can kobolds and orcs, for example, team up so that the kobolds distract and allow the orcs to get advantage on their attack rolls? Can hobgoblins Ready an action so that a PC will be attacked as soon as he or she appears around a corner?
Or should NPC and monster actions be limited to those in their stat blocks?
NPCs and Monsters can use all of the actions contained in the PHB;
DMBR06 Actions: When a monster takes its action, it can choose from the options in the Actions section of its stat block or use one of the actions available to all creatures, such as the Dash or Hide action, as described in the player’s D&D basic rules and the Player’s Handbook.
That will make intelligent monsters and NPCs a force to be reckoned with. Thanks.
If you were asking about not just rules but frequency of how much they use it:
Depends entirely on the situation, as well as the group. If the table wants a rough "no punches pulled" sorta campaign, then Ogres, wolves, and oozes are tactical geniuses. If the DM wants a close game without slaughtering everyone, he may overrun the PCs with monsters but play them dumb. The easiest thing to do is find a middle ground and try to play them as "realistically" as possible (according to stats, generalizations, and lore). Animals will either go for the weakest (looking) character or the one who hit them last. Hobgoblins will use superior tactics. Goblins will try to overwhelm you with numbers but run away the second the lose the upper hand. Orcs blindly run into battle and swing savagely at whatever's in front of them. The NPC Knight will personally challenge the party's Fighter to solo combat while his minions deal with the party. That sorta stuff.
Personally, I find it a misleading phrasing calling them PC tactics, since they're just, well, tactics! 
Unless you're talking about a player (or several) who use/abuse a mechanic so much that you throw it at them in a "How do YOU like being perma-grappled?! Or Power Word Kill'd?!" sorta way. If that's the case take a step back and not take things so personally 
No, I was just thinking about the effect of Help, especially. A dozen kobolds will now make 6 orcs look so much better if they combine so that the kobolds distract and the orcs get advantage on their attacks. It may not be that much better having 6 orcs attack with advantage, 6 kobolds attack normally and the other 6 give up their action to Help the orcs (or other kobolds), but it could be effective. Not sure why kobolds and orcs are teaming up, either, but they serve for the example. 
Highly militarized enemies would reasonably utilize tactics, such as distracting enemies and as noted players should expect it. If the orc is fearsome enough, he may bully the kobolds into distracting the party ("get in his way, grab his legs, or you're in the meat pot tonight!") but I wouldn't expect certain monsters like selfish, chaotic goblins to cooperate keenly without some form of training or divine orc meat pot inspiration.
El_Condoro wrote:
In many cases, there is no need for tactical monsters to use the Help Action in order to gain advantage, as they have their own racial method of gaining advantage reliably. In respect to Kobolds, that ability is called Pack Tactics (an ability they share with wolves, and several other creatures), and it is far superior to the Help Action in all respects.
Pack Tactics
- The Kobold has advantage on an attack roll against a creature if at least one of the kobold's allies is within 5 feet of the creature and the ally isn't incapacitated.
Hobgoblins are unlikely to use the Help Action to grant their allies advantage (except against the most heavily armored/nimble of foes) - as statistically, they deal more damage by simply flanking an enemy with a friend, thanks to their Martial Advantage ability.
Hobgoblins are also likely to employ the use of (dire) wolves as allies. While the wolves benefit from pack tactics, gaining advantage on their attack rolls, the Hobgoblins gain advantage on their melee weapon attacks thanks to the Wolf's tripping bite attack.
Martial Advantage
- Once per turn the hobgoblin can deal an extra x (xd6) damage to a creature it hits with a weapon attack if that creature is within 5 feet of an ally of the hobgoblin that isn't incapacitated.
It is all about how you design an encounter. Look for synergies betwen the baddies.... Oftentimes, the Help Action is an inferior choice for enemy units, especially in respect to those with the intelligence (or training) to use such an action.
I base a lot of that on the group the PCs are fighting. A pack of wolves is a cohesive unit, but a group of Ogres? Meh. Ogres don't strike me as tactical geniuses and rarely work together.
In other cases I've had pairs of goblins try to tackle PCs to try to knock them down (one helping the other) if they are having a hard time hitting so that the rest of the group gets advantage. Admittedly it was in a situation where the goblins did not have the option to run away or hide ... which is what they would normally do.
I base cooperation on the monster, the intelligence/wisdom or just because thematically to me it makes sense.
So yes, sometimes they use such tactics but it depends on the monster and the scenario.
Of note: Help action only helps 1 person 1 time. It's ambiguously worded enough so that the Kobold can distract the fighter so that the Orc can get in a good hit, instead of "wasting" the action on a goblin's crummy dagger.
So Help is indeed very nice, especially if they have troubling hitting or have powerful masters. But it's not "one Help action gives Advantage to everyone who attacks that character for a full round." And, as Kalani said, that may be an inferior choice for baddies with pack tactics (or similar abilities) or spellcasters with save spells
iserith wrote:
Theros wrote:
I think it depends on what you mean by tactics
FrogReaver wrote:
The typical monsters should not suddenly become a coordinated assassination squad just because the PCs showed up.
But military-inclined monsters should be a tougher smarter fight than a swarn of solo-stunt artists.
Wild beasts should do what they do best until it hurts more than it tastes good.
Once in a great while - when the plot accomodates it - the PCs CAN face a coordinated assassination squad who has trained / prepared for them personally.